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