To get this achievement you have to execute the enemy in every way possible.

Bow Hit: B while holding torque bow

Curb Stomp: need i say anything

Head Slice: y while holding torque bow

Fooooooooore: B while holding shot gun

Lancer Kill: B while holding lancer

Crack: A while their down,then X

CPR: y while their down

Pistol Hit: Y while holding boltok pistol

Shield Kill: Y while holding boomshield

BAM: y while holding longshot rifle

Whack: B while holding longshot