Here is the full list of all 20 Tentacles: Enter the Mind achievements worth 200 gamerscore.
You picked up 3 tombstones without dying.
You completed the Libido Layer!
You just bought yourself some more time!
You found the loophole in the knife
You selectively killed Kamikazes without killing any other creatures!
You held three rubber duckies at once!
Wow, a Kamikaze orbited you!
You cracked your first egg!
Go from one pitstop to the next without killing any enemies.
Get 5 snipers to aim at you simultaneously.
Attach all three tentacles to the oscillator screen on the science box
Use all 3 powers.
Equip the rainbow trail and the pink eye.
Kill 5 enemies with 1 bomb.
Crack a purple egg.
Crack a black egg.
Kill a Rammstein without using any powers.
Complete the entire Regret Layer.
Reach a multiplier of 8.
Reach a multiplier of 10.