The Ram is the enemy with a hard shell that blindly charges or rolls at you, and can be deflected with the Bash move.
The Stomper is not an enemy or a move, but rather an environmental danger, which is a stone pillar that crushes the ground when you walk under it.
The easiest location for this achievement is in the Moon Grotto, down and to the left of the spirit well, indicated by the map below. Just lure the Ram to charge at you under the Stomper pillar, defeating it, and the achievement should pop!
https://imgur.com/cjPWla3