The class Porthus crawled to level 89 in - and, apparently, the class that produced the Dungeon Anarchist's Cookbook's second edition.
Listed first in Porthus's exit record: Class: Rogue, top level 89. It fits everything else about him. Rogues survive by not being where the monster is, which is exactly how he got off the Tenth Floor - jumping into the exit while Menerva's foot was still stuck.
The class also links to two of the chapter's other details: the guard post at the Rogue Club he is offered and declines, and the Dungeon Anarchist's Cookbook, the crawl's manual of traps, sabotage and explosives, whose second edition he wrote. In the guild's Zero Zone the class is worth nothing at all.
A crawler class documented in an exit record, tying Porthus to the Cookbook's sabotage tradition and to the Rogue Club offer.