How to Unlock Hidden Archetypes
Engineer
[N’Erud] – Found outside the map (4 stalagmites mark its location on the edge of the fog).
Summoner
[Yaesha] – Purchased (15 essences) at the Bloodmoon altar.
Alchemist
[Losom] – Walk near large drain openings until you get pulled in by the Manticora (fake death screen leads to a boss fight).
Invader
[Root Earth] – Use the Dreamcatcher melees weapon on the walkers’ dream.
Archon
[The Labyrinth] – Presumably hidden behind the labyrinth red corrupted door requiring a key that will only reveal iteself by being corrupted in the labyrinth.
Explorer
Just beat the game.
In some sources it says “corrupted master key”, and in some point of story I remember aim when aiming at Keeper turns yellow (not green or red), and we get our Biome key from him, so… Maybe we can fight with him somehow at this point (using fragmented mod?) and get “corrupted master key”?..