Statistically, their hp would be 121 at a total of 39 levels.
Their thief skills would be those of a 9th level thief. Hmmm, what are their weapon and armor restrictions? As good as I thief as I recall.
Let's see, 39th level fighter on a statistical average is going to have 145 hp and a much better THAC0, will be attacking twice per round and sweeping most mundane creatures in attack. I guess a better comparison would be a ranger.
A 39th level ranger will have 110 hp on statistical average and in other ways will be like a fighter, with the addition of 3 levels of druidic spells and 2 levels of mage spells. They seem kind of broken, too. To be honest, all super hero characters are broken.
