The Walker achievements

Avoid taking damage from oil barrels in the Urban Ruin stage

Kill [5] enemies with headshots

Kill [30] enemies

Clear any stage in without taking damage

Complete all stages on the First Difficulty

Receive a flying attack from a ghoul

Shoot armored soldiers in the foot to make them stumble

Receive "Godlike" score for all stages in the Second Difficulty

Kill [300] enemies with headshots

Complete all stages on the Second Difficulty

Receive "Godlike" score for all stages in the Third Difficulty

Kill 200 enemies using the Ice Talisman