This is a pretty fast and safe way to beat the bat boss. Jump and spam light attacks. As soon as you see his tongue sticks out, about to attack you, you dodge by pressing down. Doing this will keep him engaged and he won't summon his Bitey Bats, so you can repeat this until he dies. In this insane mode, his tongue is a one-hit kill. If you mess up, you're dead. But I said this is "safe" because there're no Bitey Bats to bother you.