Here is the full list of all 26 Hellcoming achievements.
Find 15 ducklings (school)
Find the first cat (school)
Press the button in the basement (school)
Find 15 glass balls (sanatorium)
Еxorcise the demon (sanatorium)
Find the second cat (sanatorium)
Lose the game (sanatorium)
Extinguish the hellfire (sanatorium)
Step into the trap (sanatorium)
Burn the eye with a uv lamp (sanatorium)
Burn flies with a UV lamp (sanatorium)
Clean the abomination with a vacuumer (sanatorium)
Kill the hellish spider with a shocker (sanatorium)
Clean the abomination with a brush (sanatorium)
Еxorcise the demon (school)
Burn the voodoo doll in the furnace (school)
Clean the abomination with a vacuumer (school)
Heal yourself with an injector
Burn the tool in the furnace
Burn the adrenaline injector in the furnace
Lose the game (school)
Step into the trap (school)
Burn the spider with a UV lamp (school)
Burn cockroaches with a UV lamp (school)
Clean the abomination with a brush (school)
Kill the hellish rat with a shocker (school)