Sir Shovalot

From the Super Mario Wiki

A Sir Shovalot is an enemy featured in Mario vs. Donkey Kong. These baddies could not be lifted, let alone defeated. Their main goal was to shove Mario into a wall and flatten him. However, Mario could take advantage to this situation. If there is a Sir Shovalot and a small hole that Mario could not normally fit through, he could duck, and the baddie would shove him under, allowing him to get to places he wouldn't normally have been able to go before.