Here is the full list of all 38 Red Haze achievements.
Got Ending L!
Got Ending U!
Got Ending S!
Got Ending H!
Got Ending W!
Got Ending T!
Got Ending Y!
Got Ending C!
Got Ending R!
Got Ending Q!
It gets worse here everyday!
Got Ending G!
Got Ending I!
Took Starry's dress for your own.
Got Ending M!
Got Ending F!
Failure is always an option.
Got Ending O!
Got Ending Z!
Got Ending V!
You decided to strut your stuff.
Got Ending J!
Listened to a Cassette Tape.
Got Ending N!
Got Ending K!
Met up with Aunti G.
Got Ending P!
Got all 26 endings in Red Haze and went through the Alphabet Door.
Got Ending A!
Got Ending B!
Got Ending D!
Got Ending E!
Got Ending X!
There's a lot of secrets, but this one might just be the most well hidden...
Exit: Hope
Saved 1000 times total and went to the Save Shrine afterward.
Defeated the Abomination.
Went to the Other Place.