There are a couple of posts in UOHall which suggest we should not take Pixies or Promethoids as pets. I have been on one visit when the Boss kept healing and proved impossible to kill. I cant remember if Pixies or Promethoids were there then but it seems prob. The suggestion is that either/both pets are responsible for healing the Boss and making him invulnerable. There is also a suggestion that some people have not read the fiction and do not realise that ONLY pets can kill the Boss. Spellcasting in an attempt to damage him may also be having an effect.