Here is the full list of all 14 Collisus achievements.
A Fully-Lined Kevlar Suit
Looks good on you +3 coins
NOT A CAT TOY
Get 100 Kills
Get 500 Kills
Get 900 Kills
Get 1250 Kills
Get 2000 Kills
Get 5000 Kills
Get 10.000 Kills
Get 25.000 Kills
Get 50.000 Kills
Get 100.000 Kills
Gun-Fu Takedown