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