Avenging Spirits. When I was younger, a friend and I loaned each other a bunch of our games. Sadly, he ended up moving away before we managed to swap back, and he got the better end of the deal when it came to the games. However, I did get left with a copy of Avenging Spirits... the game is a bit strange but its very fun and the sprite work is just adorable.

The game has you playing as a spirit who can possess enemies. You start off with a few you can possess, and then you gain more choices as you progress. Or so I believe... I wasn't all that good at the game back in the day, so I don't remember getting too far in it.