Here is the full list of all 30 The Elephant Collection achievements.
Input Pi on Stage 25 extremely quick [in 8 seconds or less] in This is the Only Level 3
Beat your first Rave in Elephant Rave
Unlock the Velociraptor skin in This is the Only Level 2
Play Call Me Maybe On the Piano (CEFECCEDDC) in Achievement Unlocked 2
150x Final Rave in Elephant Rave
Reach combo 20 hamsters while wearing the pirate hat in Achievement Unlocked 3
Collect 100% Achievements in Achievement Unlocked 3
Buy exactly 50 pellets at once in Achievement Unlocked 3
Complete Run Elephant Run in Insane Mode
Complete Run Elephant Run in Hard Mode
Spell the only English word you can with all seven letters in Stage 14 [Curable] in This is the Only Level 3
Complete This is the Only Level 3
Hit 25% complete before leaving the first floor in Achievement Unlocked 2
Collect 100% Achievements in Achievement Unlocked 2
Complete Run Elephant Run
Build an army of 10 Miniphants in Elephant Quest
Defeat Wooly in Elephant Quest
Reach Elephant Level 12 in Elephant Quest
Find Stage 31 of This Is The Only Level 2
Clear Stage 30 in This is the Only Level 2
Unlock Rapidfire mode
Unlock Reverse Mode in Obey! The Game
Clear 60 Stages in one game in Obey! The Game
Complete This is the Only Level
Clear Stage 15 in This is the Only Level
Clear Stage 5 in This is the Only Level
Achieve 100 percent of Achievements in Achievement Unlocked
Achieve 50 percent of Achievements in Achievement Unlocked
Achieve 25 percent of Achievements in Achievement Unlocked
Lose your memories in Elephant Rave