Invisble/non-existent farportal boss

[Leverkuhn]

On the second level of the farportal I'm currently exploring there's a strange bug. There's a continuous stream of projectiles emanating from a tile three steps to the right of the stairs up which the log claims are from "Eliraba the bandit lord." In all other ways, this enemy doesn't seem to exist: I can't see him, and I can move onto his tile and launch attacks and aoe's without doing any damage. Unfortunately, since I've explored the rest of the level and found no stairs down, he seems to be the final boss, and must be killed to generate the portal home. Any way I can continue this game without breaking farportals?