Okay, I won against the singleplayer bot! I tried all the characters, but for me the strongest was still default, that power shot with the large hitbox was very powerful, especially at the edges. Although I guess against real players it might not be as easy, but we'll see.
Gameplay-wise everything felt good, the effect, the bonks, the slashes, if there was one feedback I'd give it would be to decrease the windup to the slash move, that seems pretty long. I see why it is in, because otherwise it would be too similar to the standard bounce, but I think it would feel better if there was a more immediate response to that move. Or maybe not, I dunno. One thing I'd like to praise is the variation in the designs of the characters and their special moves, I could see different people finding different characters useful, the ninja was my second favorite, he had that cool lunge special move (and some others that should come in handy against human opponents), or the wizard with his walls (although I felt the AI avoided them pretty handily).
So yeah, very fun, can't wait to test the multiplayer and become the one true rollback pong champion.