Here is the full list of all 33 Prisoner achievements.
Unlock Stage 4
Unlock Stage 5
Complete the game
Complete the game 5 times
Complete the game 10 times
Complete Trial of Death
Complete Trial of Life
Complete Uber Complex
Complete Trial of Time
Complete Trial of Darkness
Complete the game with 2 active trials
Complete the game with 3 active trials
Complete the game with 4 active trials
Complete the game with 5 active trials
Find a Secret Room
Find 10 Secret Rooms
Find 25 Secret Rooms in the New Complex
Pass 100 rooms
Pass 250 rooms
Pass 500 rooms
Pass 25 extra rooms
Find the secret way in extra room
Complete all achievements
Unlock Stage 6
Activate the Mystery Mechanism
Activate the 50 Mystery Mechanisms
Reach the 25 rooms in Endless Complex
Reach the 50 rooms in Endless Complex
Reach the 75 rooms in Endless Complex
Reach the 100 rooms in Endless Complex
Collect 3 character skins
Collect 6 character skins
Collect all character skins