Here is the full list of all 20 Tentacles: Enter the Mind (Windows) achievements worth 200 gamerscore.
Sweet, you found the knife loophole!
You held three rubber duckies at once!
You just bought yourself some more time!
You cracked your first egg!
Go from one pitstop to the next without killing any enemies.
Have a Kamikaze orbit Lemmy
Get 5 snipers to aim at you simultaneously.
Complete the Libido Layer.
Attach all three tentacles to the oscilator screen on the science box
Use all 3 powers.
Equip the rainbow trail and the pink eye.
Kill 5 enemies with 1 bomb.
Kill 10 Kamikazes without killing any other creatures.
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.
Pick up 3 tombstones without dying.