Here is the full list of all 20 Tentacles: Enter the Mind (Windows) achievements worth 200 gamerscore.
You cracked a black egg!
You killed a Rammstein without using any powers!
You grabbed the oscilator really tight
You equipped the rainbow trail and the pink eye.
Nice, you killed 5 enemies with one bomb!
You reached a multiplier of 10!
Wow, a Kamikaze orbited you!
You went from one pitstop to the next without killing any enemies!
Wonderful, now Dr. Phluff has no regrets!
You were the target of five snipers at once!
You reached a multiplier of 8!
You held three rubber duckies at once!
Great, you used all of your powers!
You cracked a purple egg!
Sweet, you found the knife loophole!
You completed the Libido Layer!
You selectively killed Kamikazes without killing any other creatures!
You picked up 3 tombstones without dying.
You cracked your first egg!
You just bought yourself some more time!