First of all, I believe that since they are bosses, they should have a health bar, that way we could know the progress of dealing damage to a boss.
The zombie boss is broken, well, at least in comparison to the other bosses in the dungeons. In prison, the boss section for the zombie is very small and difficult to deal with, speacially since this boss is very fast.
Also there are difficulties with the golem and witch dungeon, since the witch dungeon has got a skeleton boss and the golem dungeon brings you to the skeleton dungeon. (i got more than 5 skeleton heads now xd)