Horn Rabbit

One-Eyed Owl (Japanese Name) is a race of monsters that was shown in the spin-off manga series known as, The Ways of a Monster Nation. It is known to reside in Tempest inside a dome which Rimuru made to mimic a forest. They can be seen as quite strong as they are able to knock down a tree by charging and ramming its horn into the trunk.

Appearance
As its name suggests, it appears to be a normal rabbit though has a single horn from the top of its head.