250 is right, but cast the scroll of undead protection
after he changes, otherwise he will not change and you cannot kill him. Protection from Magic scroll is fine however. Also Chromatic Orb is useful, as it can kill/ petrify Kangaax with one attempt, once his magic resistance is lowered. Also, pickpocket him before killing him and you get 2 of his rings.
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Never accept an invitation from Wolfgir to a BBQ!