Here is the full list of all 29 Mega City Police achievements.
Beat the game on normal difficulty in classic mode
Beat the game under 15 minutes in classic mode
Clear the Mega-Corp level
Clear the Japantown level
Find 10 collectables
Impale 100 enemies to death
Clear the Ruins level
Clear the Contruction Site level
Clear the Suburbs level
Get killed
Complete the tutorial
Beat the game on hard difficulty in classic mode
Beat the game on extreme difficulty in classic mode
Kill 1000 enemies
Kill 100 bosses
Gather $1,000,000
Unlock 10 skins
Blast 100 enemies into pieces
Electrocute 100 enemies to death
Pulverize 100 enemies into a mist
Irradiate 100 enemies to death
Decapitate 50 enemies
Kill 50 enemies by throwing a melee weapon
Cause 50 enemies to die by fire
Kill 5 enemies with a car's explosion
Beat the final boss without taking damage