Restructure Gehennom to be very short, containing the Valley, the three Wizard’s Tower floors, and a “nexus” floor at the bottom, containing the vibrating square and four magic portals, each leading to a randomly selected demon lair.

You can only enter each lair once: you must decide whether to attempt defeating the demon lord or not before leaving. The exit portal won’t work if invocation items are left behind. The demon lords are beefed up from vanilla, and are not bribeable since they’re not guarding access to the stairs to extort passage.

As incentive for defeating the demon lords, they apply debuffs on the ascension run, described in #3396.