Bat Pat season 1 episode 22

Episode title: Puppy Love

The kids and Bat Pat discover a cute stray puppy and take it home with them. The puppy loves to play fetch, but the first time Leo is alone with the puppy, it barks and its head morphs into a terrifying demon dog. Leo tries desperately to make the puppy bark in front of the others to show them the transformation, but the puppy never does.