AT requires a 2D6 sneak attack, so you need a few levels of Rogue (or maybe Shadow Thief or Assassin). My current character is heading that way-- he's a halfling Rogue2/Transmuter2. Basically, he'll be a somewhat gimped wizard, but with some basic thiefy skills and good diplo/bluff. I'm targeting him at Wiz5, Rog3, AT(the rest), but I might be tempted to get a 4th rogue level for Uncanny Dodge.
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dang, forgot the sneak attack....well, if taking rogue levels is unavoidable, i guess i'll stick to my tiefling wiz.