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While in the Dwarven Mines, I experienced Bug report 746 - Black beast survives the crusher and gets stuck under it and was subsequently killed by it when I went to loot/inspect it, and so assumed that the crusher simply wasn't intended to kill the creature; instead I just booked it into the office and got it stuck on the door so I could get the key and flip the lever, and juked around it after opening the door again. I flipped the lever back in the crusher room and baited it into the lava. While exploring the rest of the area, I never encountered a second Black Beast and returned to Arx, having finally explored everything available before progressing the story.

I investigated Falan Orbaplanix's room and as a result could start the quest to rob Gary's bank; only, after getting the key mold from Greu I went back down to the forge only to discover that the only door to the forge/mine section now apparently has a new deadbolt or something, since the keys I had to get in/out of there no longer work, and the tunnel was still collapsed during my escape. I have no idea whether it's a result of the order I explored in, or if it's the Black Beast gaffe, or what.