The ability card is up but I can't link it here. First impression is that I'm not overwhelmed. He seems decent, but it really depends on a few factors that we don't know about yet. For instance, on his Eternal Servant ability, do you have to take a full action to resummon the creature? If so, its not that impressive. Saves you on spellbook points and that's about it, although it does give a creature Piercing +1 for free, which is decent.
As for the Plague Master, it says creatures with a "Poison counter". So...that means Cripple, Tainted, and Weak and that's it? A bit limited if so. It should have been able to be triggered off of Poison Enchantments too, and it kind of irks me that it doesn't.
Poison immunity is nice though.
All in all he seems pretty cool, but not quite as exciting as I had hoped.