Paladin ultimate

[impy]

It doesn't have to be that bad actually. I assume you mean impossible no kiting game in order to make it challenging. Getting to Verona would be a pain, but after that.
I would pick mage character, heavily intellect oriented, a from middle game demolish everything with spells, hopefully. With teddy bears being sitting ducks going bzzz
One could get all the way to Ktahu in my opinion, Ktaku and Baal I cannot tell.