Despite being the end of a saga, Dark Souls 3 does not have a definitive or canon ending.
All four endings in-game are legitimate in their own right and require quite a bit of effort to unlock.
Triggering To Link the First Flame is easy enough.
Simply:
From there, youll have no other option but to link the first flame.
The Untended Graves can be accessed by breaking down an illusory wall in Oceiros boss arena.
The Graves are ultimately just a darker version of the Cemetary of Ash with Champion Gundyr replacing Iudex.
Unkindled
Theres actually a branch ending tied to The End of Fire.
Unkindled is a particularly sadistic ending that doesnt even get a Trophy or Achievement, but its fitting.
From here, youllcross paths with Anri again at the Church of Yorshka Bonfire for one last conversation.
After killing Pontiff Sulyvahn,speak to Yuria in Firelink Shrine to trigger your wedding ceremony.
Speak with a Pilgrim outside Darkmoon Tomb underneath Anor Londoto obtain a ceremonial sword.
Use the sword on Anris body and the ceremony will be complete.
Back at Firelink Shrine, Yuria will urge the player to link the First Flame.
Next:Dark Souls 3: The Most Useful Boss Soul Weapons, Ranked
