I joined mob arena today and had tried the undead king class i thought i was just slicing through bosses because of that awesome sword.  But then I watched someone take out the magma cube boss with a diamond hoe in three hits.  Long story short bosses have a bug so that instead of being bosses they only are normal mobs.  Admins it wouldnt bother me if u let this the way it is but i think some people want the boss challenge back. 
Thanks,
Tiber