As the other person said, the bat can be influenced through Peaches and just like her there's also the green creature (idk what that is supposed to be)next to the sewer dungeon entrance(which requires you to have some already absorbed essences) which in return for "curing" you will gice essences of growth, then there's the various companions which grow everytime you defeat them, some static bosses like the Beast and the Bandit Boss,