Here is the full list of all 21 Kick-Ass 2 achievements.
Cross Chinatown
Defeat Black Death
Reach the Goths' Lair in the subway
Fight your way through the Goths to the subway entrance
Rescue Dr. Gravity
Cross out the 24 graffities
Find all the Wi-Fi hotspots
Defeat Genghis Carnage
Survive the clash with Mother Russia
Get rid of the Tumor
Finish off Chris D'Amico once and for all
Reach Genghis Carnage's whorehouse
Leave the subway
Reach the entrance to Headquarters
Eliminate all the enemies in the Justice Forever Headquarters
Escape with your life from the Cemetery
Chase the Tumor through the sewers
Cross Central Park
Survive the battle for Manhattan
Defeat Mother Russia
Defeat Chris D'Amico's thugs