After killing certain type(s) of monsters (such as the monarch of a throne room), a timer may start that spawns an avenging posse of related monsters nearby.

Extension of the feature in several variants where monster spawns are concentrated on the upstairs during the ascension run: occasionally, instead of spawning a monster, generate an organized group which is trying to get the Amulet, usually made up of sapient monsters (such as a group of soldiers, or a few priests of the same god, or some elves led by a couple elf-lords). Possibly, this only happens after you get back out of Gehennom and are again visible to the other gods.

A “money train” - a random event that spawns in a bunch of soldiers and giants carting chests of gold from the upstairs on a level to the downstairs.

Random earthquakes. Same effects as drums of earthquake, except not triggered by anything and not necessarily centered on the hero or anything special. Earthquakes (from any source) now can collapse diggable walls (turning them into floor spaces without pits) and drop rocks and boulders out of the ceiling. No effect in any Plane except Earth. Possibly, to limit this, a finite number of earthquakes can happen on any given level (after which it either collapses entirely, or just fails to produce more free rocks and boulders.)