Main Boss · Wailing Dunes · Caelid
Starscourge Radahn
Elden Ring Location, Recommended Level, Weaknesses, Radahn Festival & Boss Strategy
Starscourge Radahn is the Caelid shardbearer you reach through the Radahn Festival at Redmane Castle — location, festival triggers, level range, weaknesses, fight plan, summons, and rewards.
Quick Stats
- Location
- Wailing Dunes (festival portal from the plaza), Caelid
- Region
- Caelid
- Boss Type
- Main · Shardbearer
- Required / Optional
- Optional for most paths · Required for Ranni ending & DLC
- HP
- 9,572
- Recommended Level
- 55–70
- Recommended Weapon
- +12 to +15
- Weaknesses
- Pierce best · Rot strong · Holy resisted
- Runes
- 70,000
- Drops
- Great Rune · Remembrance
- Festival Requirement
- Altus Site of Grace, or Ranni / Blaidd / Iji festival route
Starscourge Radahn Location
The Wailing Dunes fight only opens through the Radahn Festival at Redmane Castle in Caelid.
Quick Answer
Location: Wailing Dunes arena via Redmane Castle festival, Caelid
Nearest grace: Chamber Outside the Plaza. After the kill, Starscourge Radahn (arena grace after the fight) appears in the arena.
Radahn is fought in the Wailing Dunes of Caelid, but you only reach the arena after the Radahn Festival starts at Redmane Castle. The nearest rest before the portal is Chamber Outside the Plaza; after the kill, a Starscourge Radahn Site of Grace appears in the dunes.
From Impassable Greatbridge, cross into Redmane Castle (or take the waygate on the bridge once it is active), clear or skip the courtyard route to Chamber Outside the Plaza, speak with Jerren when the festival is live, then take the plaza portal into the Wailing Dunes.
Region
Caelid
Castle
Redmane Castle
Exact Area
Wailing Dunes (festival portal from the plaza)
Nearest Site of Grace
Chamber Outside the Plaza
Boss Arena
Open desert dunes with buried weapon clusters and summon signs
Game
Base Game
Starscourge Radahn location map
Map location
Chamber Outside the Plaza
Pre-fight rest: Chamber Outside the Plaza at Redmane. The Starscourge Radahn grace appears in the Wailing Dunes only after the kill.
How to Get to Starscourge Radahn
- Caelid
- Impassable Greatbridge
- Redmane Castle
- Activate Radahn Festival
- Chamber Outside the Plaza / Festival Plaza
- Portal into the Wailing Dunes
- Starscourge Radahn
Step 1
Reach southern Caelid and the Impassable Greatbridge Site of Grace east of the swamp approaches.
Step 2
Enter Redmane Castle from the bridge side (or use the bridge waygate once festival traffic is active).
Step 3
Progress to Chamber Outside the Plaza — the nearest grace before the festival plaza and boss portal.
Step 4
Confirm the Radahn Festival is active (plaza NPCs, Jerren’s war speech). If the castle is still a normal dungeon, finish a festival trigger first.
Step 5
Talk to Castellan Jerren in the plaza, step onto the festival portal, and load into the Wailing Dunes for Starscourge Radahn.
Nearest Site of Grace
Chamber Outside the Plaza is the rest point before Jerren and the festival portal. Starscourge Radahn (arena grace after the fight) only appears once Radahn is dead.
How to Start the Radahn Festival
The Wailing Dunes stay locked until the Radahn Festival is live at Redmane Castle.
Radahn Festival Trigger Requirements
Altus route: rest at any Site of Grace on Altus Plateau (Grand Lift of Dectus arrival, Ruin-Strewn Precipice exit, or any other Altus rest). One grace is enough.
Ranni route: enter Ranni’s service at Ranni’s Rise, speak with Blaidd, Iji, and Seluvis at the three towers, then talk to Blaidd in Siofra River about Radahn — or ask Iji about Jerren when that option appears.
Either path starts the Radahn Festival at Redmane. You still have to travel to the castle and take Jerren’s portal; finishing the requirement alone does not put you in the dunes.
How to Activate the Radahn Festival
Step 1
Complete one valid trigger (an Altus grace, or the Ranni → Blaidd Siofra / Iji Jerren line).
Step 2
Travel to southern Caelid and the Impassable Greatbridge Site of Grace.
Step 3
Enter Redmane Castle from the bridge (or the bridge waygate once festival traffic is up).
Step 4
Confirm the plaza has shifted to the festival: gathered champions, Jerren’s war talk, dungeon invaders gone from the square.
Step 5
Rest at Chamber Outside the Plaza if you need flasks, speak with Castellan Jerren, then step onto the plaza portal into the Wailing Dunes.
How to Activate the Radahn Festival Early
Skip Altus entirely by taking Ranni’s early path. Reach Ranni’s Rise (Caria Manor is the usual door), speak with Ranni, and accept her service.
Talk to Blaidd, War Counselor Iji, and Seluvis in the three towers beside the rise so their later dialogue options appear.
Go down to Siofra River and find Blaidd on his hunt. Finish the conversation where he ties the sealed stars to General Radahn — that is the usual way to start the festival early.
If you are already at Iji’s road forge north of the manor, ask him about Jerren and the festival when the option is available. Same result, fewer underground steps.
Then travel to Impassable Greatbridge or Redmane. Starting the festival early only opens the event; Radahn still fights like a mid-game shardbearer.
Radahn Festival Not Starting?
If Redmane still plays like a normal castle with knights and a plaza fight, the festival has not started yet — rest at an Altus grace or finish the Blaidd / Ranni step.
Already visited Altus but the plaza looks empty? Rest at a Redmane grace, reload, or fast-travel away and back so the castle can update.
Before the festival, Redmane has its own enemies and loot. Clearing it first is fine; once the festival begins, the plaza switches over to the war gathering.
You cannot open the Wailing Dunes portal from outside without the festival. The fight is behind that event, not behind a fog wall out on the open sand.
Starscourge Radahn Recommended Level
A fair mid-game window for the festival fight. Come hotter if Caelid itself is still shredding you.
| Recommendation | Value |
|---|---|
| Character Level | 55–70 |
| Vigor | 30+ |
| Standard Weapon | +12 to +15 |
| Somber Weapon | +5 to +7 |
Treat 55–65 as a fair first clear if you use festival NPC summons and Torrent. Push into the high 60s or 70s if Caelid soldiers and dogs are still deleting you on the road in.
Vigor matters more than raw level once arrows and gravity pulls start landing. Melee wants enough HP to survive a missed roll into a double-blade combo; mages want flasks and space more than an extra damage stat.
Weapon upgrade level is the real gate. A +12/+15 standard (or +5/+7 somber) with status or pierce does more for this fight than five unspent levels.
Recommended Level Without Summons
| Recommendation | Value |
|---|---|
| Character Level | 65–75 |
| Vigor | 35+ |
| Standard Weapon | +15 to +18 |
| Somber Weapon | +6 to +8 |
Without NPC summons, plan closer to 65–75 with a finished mid-game weapon and tighter dodge habits. You still have Torrent — solo here means no festival signs, not no horse.
Scarlet rot, bleed or frost from range buy time while you learn his blade strings. Do not open the fight barehanded against the arrow volley just to prove a point.
Starscourge Radahn Weaknesses
What damage types hit hardest, which statuses build, and what to leave in the chest.
Damage Weaknesses
| Damage Type | Effectiveness |
|---|---|
| Slash | Slightly resisted |
| Strike | Slightly resisted |
| Pierce | Full damage · best physical |
| Magic | Resisted |
| Fire | Resisted |
| Lightning | Resisted |
| Holy | Noticeably resisted |
Status Effects
| Status | Effectiveness |
|---|---|
| Bleed | Works |
| Frostbite | Works |
| Poison | Works |
| Scarlet Rot | Works · best status |
| Sleep | Works · builds slowly |
| Madness | Immune |
Best Damage Types Against Radahn
Pierce weapons and skills for raw damage.
Scarlet rot for long residual pressure while you resummon or heal.
Bleed or frost as secondary status if rot is not available.
Avoid holy-primary kits unless you have no other upgrade path.
Resistances
Pierce is the cleanest physical answer — spears, thrust swords, and piercing weapon skills beat his slight slash and strike padding.
Holy is his strongest defense. Magic, fire, and lightning all hit softer than physical pierce; still usable if that is your build, just slower than pierce or a stacked status plan.
Scarlet rot builds fastest. Bleed, frost, and poison also work; sleep is slow; madness does nothing.
He is not weak to gravity just because he uses it. Bring rot pots, arrows, or a thrusting weapon and play the arena — do not mirror his sorceries unless your kit is already built for them.
How to Beat Starscourge Radahn
Torrent, festival summons, the meteor transition, and clean melee, mage and solo plans for a first clear.
Quick Strategy
- Call Torrent immediately. Sprint the opening arrow rain using dunes and buried weapon clusters as cover, and plant the first wave of NPC summon signs as you close.
- Fight under his legs or on his flanks once melee range opens. Stay mounted for gap closes and big gravity swings; hop off for safer free-aim hits if you prefer.
- Keep summons in the fight as rotating cover — ride the arena and call fresh signs when bodies drop. Several NPCs can be active at once; more signs sit in groups across the sand.
- At ~50% HP he leaves the map and crashes back as a meteor. Sprint away on Torrent the moment he launches; the landing deletes anyone under the impact.
- Phase 2 adds floating rock volleys and aggressive charge spins. Same plan: summons up, pierce or rot damage, punish recoveries, never greed through a full blade string.
Before the Fight
Aim for level 55–70 with a +12/+15 standard weapon or +5/+7 somber. Get Vigor to 30 or higher before you treat the bow phase as optional.
Equip a pierce weapon or something that applies rot or bleed as your default. Leave holy-first kits behind unless you have no better upgrade path.
Fill HP flasks first. Keep at least one FP flask if you will cast Rotten Breath, throw pots, or lean on weapon skills.
Scarlet rot pots or arrows help. Bring Exalted Flesh or whatever body buff you already trust. A fire-defense liver is optional — surviving the meteor is mostly about running clear, not stacking negation.
Rest at Chamber Outside the Plaza, tidy the pouch, and decide before the portal whether you will use festival summons. It is easier to call them again mid-fight if that choice is already made.
Opening the Fight
You load in facing a long dune approach. Radahn is already drawing the greatbow on the far rise — the first stretch is a ranged gauntlet, not a fair melee duel.
Mount Torrent right away. Gallop in wide curves; riding straight into Rain of Arrows and gravity arrows is the usual early death.
Weapon piles stuck in the sand block gravity arrows until they break. Duck behind one if a homing shot is locked on, then move before the next volley shatters it.
Golden summon signs sit on the approach and along the flanks. Call Blaidd, Alexander, Lionel, Therolina, or whoever is available before you settle under the horse.
Only commit to sword range once you are close and at least one summon is up. Trading arrows on foot with a slow weapon is how runs die before the real fight starts.
Phase 1
Once you are under him, phase 1 is cavalry blade strings, Cragblade spikes, gravity pulls, and the odd bow shot if you drift too far away.
Stay near the rear legs and hip. Standing in front trading light attacks into double-blade sweeps and tramples is how most melee attempts end.
Blade Sweep Combo: wide left-right sword hits from horseback. Stop your own combo by the second swing, roll into the later hits or pass under Leonard, then take one jump thrust or two lights on the finish — not a long skill.
Cragblade: gravity gathers on a sword, then stone spikes burst up through the sand in a line. When the blade loads dark purple, sprint sideways on Torrent instead of blocking in place.
Gravity Pull: sand and lock-on drag you inward. Peel off to the side on horseback the moment the pull starts. Holding block through it drops you into a free blade follow-up.
Collapsing Stars: inward gravity coils on you or a summon like a grab setup. Gallop sideways, then close again only after the coil drops.
If every summon falls, do not hold the center alone. Loop the dunes, call fresh signs, and come back in with help. Phase 1 rewards patience more than raw damage.
Phase 2
At about half health he howls, launches straight up, and leaves the arena. That is the meteor transition — gallop away immediately and keep your eyes on the ground, not the sky.
The crash wrecks anything under the impact. If a summon is still mid-field, let them take it; your job is to be outside the blast, heal if you were clipped, then call signs again.
After he stands, four rocks rise beside him and launch at you or your summons. Keep moving on Torrent; standing still to finish a spell under a rock is a free death.
Airborne Spin Charge: he floats, blades out, and corkscrews across the dunes. Leave early — late rolls still clip the spin. Hit him only after he lands and pauses.
His phase 1 blades and gravity tools stay in the kit, now chained faster between rocks. Same rule as before: one or two hits after a rock volley or finished spin, then get out.
A clean phase 2 loop is: keep a summon on him, wait out the rocks, thrust or apply rot on the recovery, remount before the next charge. Forcing a third light into a spin is the usual wipe.
Melee Strategy
Pierce weapons, heavy thrusts, and jump thrusts do the honest work. Fight the legs; mount up and leave when a full double-blade sweep or spin charge starts.
After Blade Sweep Combo or Cragblade finishes, spend one charged heavy or skill — not a long weapon skill that locks you into the next swing.
If you stay off Torrent after the opener, every gap close is on foot. Phase 2 rocks and spins punish slow chases hard; most melee clears still remount between hits.
Let a summon hold his attention for the heavy hit, then roll or hop back to Torrent. Greed is how mounted combos erase a 30-Vigor bar.
Mage / Ranged Strategy
Rotten Breath, poison mist, pots, or other lingering pressure beats pure glintstone trades while he gallops through magic resistance.
Cast after a summon draws Blade Sweep Combo, after Cragblade spikes settle, or when the last phase 2 rock has already launched. Stop casting if a pull or spin starts mid-spell.
Keep a piercing backup weapon for empty FP. Gravity sorceries look right on theme, but they are not a free win — status and summons matter more than copying his kit.
Solo Strategy
Without festival NPCs you still have Torrent. Path the bow phase cleanly before you take any blade trade.
Scarlet rot or bleed from range replaces the missing help. Apply once under the horse, remount, and hit-and-run while the ticks work.
Respect the meteor and the rocks. Save flasks for phase 2; spending the whole bar on phase 1 greed is the usual solo reset.
If you are still learning the moves, use summons for one clear look at the tells, then try without them once the meteor timing feels natural.
Summon Strategy
Festival summon signs are the main help in this fight: Blaidd, Alexander, Lionel, Okina, Great Horned Tragoth, Finger Maiden Therolina, Patches, and Jerren once phase 2 is live.
Ride from sign to sign on the approach and flanks. When a champion falls, loop the dunes and call another — each NPC has more than one sign, and a used sign only removes that copy.
For a first clear, call a heavy body first (Lionel, Tragoth, or Alexander), then Blaidd, then Therolina for chip damage. Patches leaves almost immediately; do not count on him as a tank.
Jerren matters most after the meteor. If phase 2 opens with nobody alive, refresh the field before you try to handle rocks and spins alone.
Spirit ashes are separate from festival signs. Summon an ash only when you have stamina and space after the portal — the dunes already get crowded with champions.
How to Cheese Starscourge Radahn
Easiest honest clear: full festival summons, Torrent, and scarlet rot or pierce damage. Call fresh signs whenever the squad falls; that is the normal festival help, not a glitch.
Rot pots, arrows, and long kiting still work if melee feels bad — apply rot, remount, and wait out the ticks while summons hold his swords.
Edge-of-arena cheeses exist (northern cliff falls; southern shore so the meteor drops him into the water). They are finicky and can break after patches — if either fails twice, stop and fight him properly.
Underleveled and only need the kill for Ranni’s path? You still have to defeat him. A cheese is just another way to get the kill, not a way around it.
Starscourge Radahn Summons
Festival NPC signs are a core part of this fight — where they appear, who shows up, and how re-summoning works.
| Summon | Notes |
|---|---|
| Blaidd the Half-Wolf | Melee summon · Ranni’s shadow |
| Alexander, Warrior Jar | Melee summon · jar champion |
| Lionel the Lionhearted | Heavy melee summon |
| Okina | Fast melee summon |
| Great Horned Tragoth | Heavy melee summon |
| Finger Maiden Therolina | Ranged support summon |
| Patches | Leaves shortly after being summoned |
| Castellan Jerren | Phase 2 festival summon |
Signs appear in groups across the Wailing Dunes, not only at the entrance. Ride the arena to call them again.
Several champions can fight at once. When a sign is used it vanishes, but each NPC has more than one sign in the field.
Festival summons are the main help here. Solo is still possible — see the solo plan under How to Beat.
Starscourge Radahn Attack Patterns
Each move with its tell, how to dodge it, and when you can punish. Learn Rain of Arrows, Blade Sweep Combo, Cragblade, Meteor Crash and Floating Rock Volley first — they end the most attempts.
| Attack | Phase | Tell | Damage | Dodge | Punish |
|---|---|---|---|---|---|
| Rain of Arrows | 1 | Greatbow angled high; arrows drop in a vertical rain on your last position | Physical | Stay on Torrent and keep galloping in curves — stopping under the rain is the opener death | None at range — only closes the fight when you reach sword range |
| Gravity Arrow | 1 | Homing purple-tinged shot that tracks after the initial volleys | Physical / gravity | Break line of sight with buried weapon clusters, then leave before the cluster shatters | After you are inside melee range and the bow phase ends |
| Blade Sweep Combo | 1–2 | Wide left-right greatsword swings from horseback across his front arc | Physical | Stop your own combo by the second swing. Roll into later hits or pass under Leonard; backing straight away still catches the tip | One jump thrust or two lights on the final recovery — not a long weapon skill |
| Trample Charge | 1–2 | Leonard drives forward in a straight or slight-curve horseback rush | Physical | Sidestep off the charge line on Torrent; rolling late from the front still clips | Short reclose on his hip after the rush slows |
| Cragblade | 1–2 | Sword loads with gravity, then a line of stone spikes bursts up through the sand | Physical / gravity | Sprint sideways the moment the blade charges purple-black; blocking in place still eats the spike row | After the last spike settles — one melee punish or a quick cast |
| Gravity Pull | 1–2 | Sand and lock-on drag inward toward him before a follow-up swing | Gravity | Break perpendicular on Torrent as soon as the pull starts; turtling drops you into free blade hits | Only if he idles after the pull — many chains go straight into a sweep |
| Collapsing Stars | 1–2 | Inward gravity coils on you or a summon like a ranged grab setup | Gravity | Lateral gallop off the coil; standing still is how you get yanked into a combo | After the coil fully drops and he is not already mid-sweep |
| Meteor Crash | 1 → 2 | At ~50% HP he howls, launches skyward, vanishes, then fiery-crashes back | Fire / impact | Full gallop away the instant he leaves the ground; do not stare at the sky under the landing | None during descent — heal, call summons again, then re-engage after the dust |
| Floating Rock Volley | 2 | Four rocks rise and hover beside him, then launch at you or summons | Physical | Keep moving sideways on Torrent; let a summon take a rock when help is up; do not stand still to finish a spell | When the last rock has launched — short melee, a rot application, or one spell |
| Airborne Spin Charge | 2 | Floats up, blades extended, corkscrews across the dunes in a long charge | Physical | Disengage early on Torrent; late rolls under the spin still clip | After he plants and takes a breath — best clean phase-2 melee window |
Starscourge Radahn Stats
First-journey values for HP, defense, poise, phases and runes. Later journeys hit harder and take more to fell.
| Stat | Value |
|---|---|
| HP | 9,572 |
| Defense | 113 |
| Poise | 120 |
| Parryable | No |
| Critical | Yes |
| Phases | 2 |
| Phase Transition | About 50% HP — meteor crash from the sky |
| Runes | 70,000 |
| Boss Type | Main Boss · Demigod · Shardbearer · Remembrance |
| Required / Optional | Optional for most paths · Required for Ranni ending & DLC |
| Festival Requirement | Altus Site of Grace, or Ranni / Blaidd / Iji festival route |
Damage Negation
| Type | Negation |
|---|---|
| Standard | 10 |
| Strike | 10 |
| Slash | 10 |
| Pierce | 0 |
| Magic | 20 |
| Fire | 20 |
| Lightning | 20 |
| Holy | 40 |
Status Thresholds
| Status | Threshold |
|---|---|
| Poison | 334 / 432 / 722 / 1179 |
| Scarlet Rot | 243 / 285 / 383 / 673 |
| Bleed | 334 / 432 / 722 / 1179 |
| Frostbite | 334 / 432 / 722 / 1179 |
| Sleep | 548 / 838 / 1295 |
| Madness | Immune |
You can finish the base game without beating Radahn on several endings. Defeating him is required for Ranni’s Age of the Stars route (the stars must move again) and to access Shadow of the Erdtree. His Great Rune also counts toward the two activated Great Runes needed for Leyndell.
Starscourge Radahn Drops and Rewards
What Radahn drops on defeat, plus short links for the Great Rune, Remembrance and Starscourge Greatsword.
Boss Drop
Radahn's Great Rune
Great Rune dropped on defeat. Activate it at the Divine Tower of Caelid, then equip it and use a Rune Arc for a large HP raise.
Boss Drop
Remembrance of the Starscourge
Remembrance boss reward. Spend it with Finger Reader Enia for the Starscourge Greatsword or Radahn's Spears, or consume it for runes.
Remembrance Weapon
Starscourge Greatsword
Remembrance weapon option from Enia. Open the weapon page for requirements, moveset, and builds.
View Starscourge Greatsword →Defeating Radahn awards 70,000 runes on a standard first journey.
His death releases the stars, opens the Limgrave falling-star crater into Nokron, and continues Ranni’s path as well as the requirements for Shadow of the Erdtree.
Radahn’s Great Rune activates at the Divine Tower of Caelid. The Remembrance trades at Finger Reader Enia for the Starscourge Greatsword or Radahn’s Spears.
Starscourge Radahn vs Promised Consort Radahn
Same legend, two fights. Starscourge Radahn is the base-game festival battle in Caelid’s Wailing Dunes. Promised Consort Radahn — later Consort of Miquella — is the Shadow of the Erdtree finale in Enir-Ilim.
In the base game you fight on open desert with Torrent, festival NPC summons, a greatbow opener, and a meteor into phase 2.
In the DLC the arena is the divine gate at Enir-Ilim: no festival warboard, a dual-wield young-lion moveset, and Miquella’s light. It is a different fight and a much harder one.
Miquella’s vow and the promised consort title still point at Radahn, but the Caelid battle is the broken general after Aeonia, not the DLC duel.
Caelid habits do not carry over. Leave Torrent routes, festival signs, and dune cheeses behind when you reach the consort fight.
Starscourge Radahn Lore
Who Radahn was before Aeonia, why the stars stand still, and what the festival is for.
Radahn is the son of Radagon and Rennala, raised to demigod stature when Radagon returned to Marika. Red hair, lion heraldry, and a lifelong imitation of Godfrey sit on top of Carian gravity study.
He learned gravitational magic in Sellia under an Alabaster Lord so he could keep riding his scrawny horse Leonard and, later, so he could challenge the stars themselves. Holding the night sky still earned the Starscourge name and protected Sellia’s fate-bound fortunes.
In the Shattering he warred from Redmane Castle as the Red Lion General. The conflict ended in the Battle of Aeonia against Malenia: a stalemate sealed when she bloomed scarlet rot into Caelid and into him.
Rot ate his mind but not his life. He still clutches Leonard and still holds the stars when you find him — a feral shardbearer devouring friend and foe on the Wailing Dunes. The festival is Jerren’s honorable answer: gather champions, end the general, and claim the Great Rune.
Keep going
Starscourge Radahn FAQ
Is Starscourge Radahn optional?
Yes for several endings and for simply reaching the capital with other Great Runes. No if you want Ranni’s Age of the Stars ending or Shadow of the Erdtree access — both require Radahn dead so the stars can move and the wider path can open.
Is Starscourge Radahn hard?
He feels brutal on foot in the bow phase and chaotic in phase 2, but the festival is designed around Torrent and NPC summons. With signs refreshed and a pierce or rot plan, most first playthroughs clear him in the mid-game band. Solo without summons is a real jump in difficulty.
What level should you fight Starscourge Radahn?
About level 55–70 with a +12/+15 standard weapon (or +5/+7 somber) is a fair summons-assisted window. Without festival NPCs, lean toward 65–75 and higher Vigor.
What is Starscourge Radahn weak to?
Pierce is the best physical type. Scarlet rot is the best status. Bleed, frost and poison also work. Magic, fire and lightning are resisted; holy is resisted more; madness does nothing.
Can you beat Radahn without summons?
Yes. Skip the festival signs and play mounted hit-and-run with rot or pierce. Expect a longer fight and stricter meteor/rock discipline. Torrent is still available even when you refuse NPC signs.
How do you activate the Radahn Festival?
Rest at any Altus Plateau Site of Grace, or take Ranni’s early path: enter her service at Ranni’s Rise, speak with the three tower NPCs, then talk to Blaidd in Siofra about Radahn (or Iji about Jerren). Once the festival is active, go to Redmane, speak with Jerren, and take the plaza portal.
Where is Starscourge Radahn?
In the Wailing Dunes of Caelid, entered from the Radahn Festival portal at Redmane Castle. Chamber Outside the Plaza is the nearest pre-fight grace.
Does killing Radahn matter for quests?
Yes. The stars move again, a falling star opens Nokron under Limgrave, and several questlines (Ranni especially) advance only after he dies. Review NPC steps before and after the festival if you are mid-quest.