Bats

Bats are really common on Arcade and Stages modes. They can only move in a Y or X axis (up and sideways) and then does the opposite, endlessly. They will kill on impact. However, when you have freeze activated, you can kill it when you move your character to it. If you touch a bird you lose a life. Also, when you die of a bird, if you regenerate, the bird will disappear.