During the last part of the zoo fight on dungeon level 13, I was experiencing weird persistent crashes. Crashed three times during that zoo fight, with no obvious direct correlations to a specific action that was causing it. The crashes started only after I'd defeated all the Red Deths and Eldritch Tubers, and was facing the horde of 30+ Witch Heads in the back of the room. Crashes only occurred while there were more than a dozen Witch Heads aware of me, and didn't happen anywhere else on the floor. Might be worth keeping an eye on some of the less-frequently cast Witch Head spells, to see if any of them are causing trouble. I don't have a save game for it, because I was able to eventually get it to finish and then I went on to kick Dredmor to the curb no more than an hour later. I can't quite rule out mod-related causes for the crash. The zoo was a totally normal main-game zoo, but I had a few skills I hadn't taken before. So don't spend a ton of debug and development time on this, it's just something to put on your radar in case you hear of others having crashes in the same level.
