None of these are probably right, but at least I took a stab at all of them.

1. Er...one?

2. I'll take a wild guess. Bolly, and his biggest bug(s) are that his only possible endtext is 0 and if you die to him and return, before you touch the activate boss event, you'll see half his sprite just floating there. The other I'm going to guess is Devil Devan, and he has the old "dies in one hit if the first phase is killed with a stomp/kick/uppercut" bug.

3. Again, a wild guess, but the duplicates are unmasked versions of their doppelgangers?

4. Ugh...I'll just say 5 and there's another colour with an unimplemented sprite. Er, or something.