I don't think anyone could name all of the Castlevania bosses that heal themselves, there's just too many, so I'll just name a few.
The Wallman in Order of Ecclesia always have an unlimited supply of Super Potions to negate the amount of damage he takes. The only way to defeat him is by sucking up his glyph.
Dracula's Soul Steal attack in Order of Ecclesia can count as well.
That's all I can think of.
Anyway, question.
Which card combination in Circle of the Moon can turn you into a Skeleton?