Here is the full list of all 35 Disc Room achievements.
COMPLETE HARD MODE
SURVIVE 20 SECONDS IN ANY HARD ROOM
SURVIVE 10 SECONDS IN EVERY HARD ROOM
EXPLORE ALL HARD ROOMS
START HARD MODE
UNCOVER THE GOLDEN MYSTERY
DEFEAT THE ULTIMATE GATEKEEPER USING EVERY ABILITY
EXPLORE ALL ???? ROOMS
SURVIVE 20 SECONDS IN EVERY ROOM
DIE FROM ALL DISCS
EXPLORE ALL ROOMS
DISCOVER THE FOURTH GOLDEN ROOM
FOLLOW THE PATH
DEFEAT THE ULTIMATE GATEKEEPER
UNLOCK ALL 6 ABILITIES
DIE FROM 4 DIFFERENT DISCS IN ONE LIFE
???? THE ????
DISCOVER THE THIRD GOLDEN ROOM
DEFEAT THE PHANTOM GATEKEEPER
WALK 10K STEPS
FACE THE GOLDEN CARCASS
DISCOVER THE SECOND GOLDEN ROOM
SURVIVE 60 SECONDS IN ANY ROOM
DEFEAT THE CARNIVOROUS GATEKEEPER
FEED ???? 4 ????
DEFEAT AND REVIVE AN ANTIBODY
HOLD DOWN FFW FOR 10 SECONDS STRAIGHT
SURVIVE 20 SECONDS IN EVERY ROOM IN ONE ZONE
DISCOVER THE FIRST GOLDEN ROOM
DEFEAT THE OVERGROWN GATEKEEPER
SURVIVE 0 SECONDS OR LESS
DIE FROM ALL DISCS IN ONE ZONE
END A RUN FROM THE MAP
DEFEAT THE ARMORED GATEKEEPER
QUIT TO MAIN MENU WITHIN 2 SECONDS AFTER DYING