What are those 3 Hidden Endings?
1. Defeat Nyx by Consuming it
2. Wearing the Mask
3. ???
I need help, someone who knows the 3rd one?
I believe you're missing the purity ending. That is from putting all the names of pure characters into the eye of the void.
Spoilers for the names needed:
Drenth: You just have to accept the mark or whatever it's called when you meet him. Don't fill him with spawn.
Torgar: Do the purity path
Lukka: Just evolve your symbiote