Crushed
From Rampage Knights Wiki
Kill 10 enemies with the Mighty Foot.
How to beat the challenge

The Mighty Foot.
Curses can be gained by drinking a Demonic Mixture, praying at a Demonic Altar, using a Scroll of Black Magic and playing cards. A random curse or disease is also given to the player at the start of each area in the Hard and Insane game difficulties. However, the curse gained is random and there is no guarantee that it will be the mighty foot.
One tactic is to stand in a group of opponents until a red circle appears, then move out of the way. The enemies will then get crushed.
Rewards
Stomp damage +20.