It would be cool to find him sleeping in his lair, and then when you hit him he wakes up, when you hit him some more he says stuff like:"OW", and "Please stop". After enough times he enters his boss mode, says something like "I think I found some more JUICE." but at the end when he says juice he says it in a scary way. Just an idea I thought would be good to ad

I agree with you

Yes.

Yes.

I'm 150% for this.

It's interesting, because he has a hitbox and can be knocked back with a swing from a mace. He even used to drop a juice blob, but it didn't give any points.

While I'm not opposed to the idea of eventually fighting the vampire bat, I saw suggestions of maybe finding him in danger and actually helping him out and I think I like that idea more. Maybe it could be a thing of you encounter him in his lair, and from there you could either fight him or leave him alive and if you leave him alive he shows up in later events.

Perhaps if there is a kill/no kill choice for something like this, you could get two things

1.  By not killing him you get more vampire suck range, or maybe when you spit something out it homes in on an enemy? It could be from him giving you a gift from one vampire to another.
2. By killing him you get a shop there - and maybe a special item, like a grappling hook because the shopkeeper has no need for it now that he is up there in the lair - perhaps with a zipline down?

Really this seems like it would come anyway for the game (at least a fight with some vampire, where you would have to fly out of the mouth or something), it is just nice thinking up hypotheticals to this cool game

I like the suggestions here about killing him or not killing him being an option.

I personally would like to be able to 100% the game and rack up juice without becoming a vampire; or else, if I must become one, to be able to cure myself of it.

If that option comes up I vote for one or the other to lead to curing of vampirism, if the player character has it.

Despite how much he annoys me by infection, though, that line about beating him up in his sleep seems too harsh, even for him.