Elden Ring: How To Beat Starscourge Radahn

gamespot.com:

The Elden Ring Radahn boss battle is among the game’s most difficult fights. Multiple instant-kill attacks, swift, unpredictable sword combos, and a nigh-unbeatable second phase make the Radahn fight one you’re better off seeking help for. FromSoftware added this help in the form of multiple NPCs that can create an opening for you to attack and bring Radahn to his knees when it’s too dangerous for you to try. Here's how to beat Radahn in Elden Ring.

You can fight Radahn at any point in the game without even having to deal with a dungeon. He’s sent summons across the land, calling for champions to fight him in the hopes of ending his Scarlet Rot-induced madness. Don’t let the ease of access fool you, though. You should be at least level 70 before fighting Radahn, ideally with a powerful weapon suited to your chosen build, such as the Moonveil Katana, or strong spells with good range, including Comet. Activate your Great Rune--Godrick’s is recommended, as ever with Elden Ring’s boss fights--and make sure your Flask of Wondrous Physik has a handy combination of buffs ready.

Once you’re ready, head to Redmane Castle in southeastern Caelid, south of Sellia, Town of Sorcery, and east of the Cathedral of Dragon Communion. Use the teleporter near the Site of Grace at the bridge to avoid dealing with the slog through the castle, and then head inside. Speak with Jerren, the old man on the platform, when you’re ready to battle, then take the elevator down to the beach.

Unlike most fights, you can summon several NPC companions once the battle against Radahn begins. Also unlike most fights, Radahn can one-shot you with his homing gravity arrows. Keep your target lock on Radahn so you can see the arrows, then dodge once they get near.