Hellblade: Senua's Sacrifice - Final Boss Fight & 100% Completion Ending

Final Boss Fight & Game Ending for Hellblade Senua's Sacrifice.
At the end of the game (before the last boss) you need to step through a portal with 44 glyphs all around it. At 100% completion (all lorestones found) the glyphs will turn white and you get a slightly different cutscene before the endboss.
Lorestone Guide:
The endboss is quite easy. You will have an overpowered sword that kills most enemies in one hit. Activate your focus ability (press R2 during combat when it's powered up) and then do L1+Square combos. This is a running sword stab. Senua will jump a few meters to the enemies. The weak ones die in just one hit. You can chain together really long combos with this and kill one enemy after the other.
You don't actually have to fight the boss himself, only his mobs. In the last phase when the boss is sitting in the middle of the arena you must let the enemies kill you. Otherwise they just keep spawning infinitely. When they kill you the final ending cutscenes starts.
There are 3 phases:
Phase 1: Fight the mobs until they are all dead.
Phase 2: Fight the shadow bosses until they are all dead. Remember to use R2 to trigger the focus ability.
Phase 3: Let the enemies kill you.
Hellblade Senua's Sacrifice Trophy Guide & Roadmap:
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All Hellblade Trophies:
Done
Collect all of the other trophies
The Fight Begins
Reaching the Gate for the first time
Extinguished
Defeat Surtr
Master of Illusion
Defeat Valravn
Source of the Darkness
Meet Hela for the first time on the Bridge
Trust Your Senses
Complete the Blindness Shard Challenge
Different Perspectives
Complete the Tower Shard Challenge
Cure For the Plague
Complete the Swamp Shard Challenge
Escaped
Complete the Labyrinth Shard Challenge
Gramr Released
Pull Gramr out of the Tree
Warrior
Escape the Sea of Corpses
Into the Mountain
Enter Helheim
Tamed the Beast
Defeat Fenrir
The Final Battle
Confront Hela
Stories From the North
Collect all of the Lorestones