Idk, saw it too

call a dog

Back when this game was on itch.io, there was an enemy called the Koaladog, which could not be killed. It used to stand outside the graveyard. I believe it was there to practice your swings and whatnot. They have now moved him to Mr. Fox's attic as a little easter egg for the OG players to find and remember about.

koala but its not mario its idk

A Koaladog you can't kill it