I can also confirm now that "breaching the underworld" is very very common. To the point that, so far (after some 300 years of game), the Underworld was breached in the same city twice. First it was breached and the demonic goblin hord took over. Then they were defeated by another civ. Then this civ breached the underworld in the same city lol
I’m a little disappointed it wasn’t the first demon civ causing the second breach without any dwarven interlopers. I wonder if that could happen though, I wonder what controls it.
You don't need a Dwarf civ to do it. Human civs are just as capable (probably needs a fortress though). Haven't seen a goblin do it yet, but unless it's hardcoded not to, it seems reasonable that they might.
I can also confirm this. The first civ was Dwarven but the second civ was Human.
Ah, just checked through a world which breached the circus 20(!) times over 300 years and I've found a case where goblins were the culprits.
The Confusing Furious Hell and their Pale Blue Brute leader were released by the goblins of The Hot Cruelty.
180 years before this, The Hot Cruelty themselves and their Buffalo Brute leader were unleashed by a Dwarf civ.
All of the breaches appear to take place in either a Fortress or a Mountain Halls.
And in the same world it happened once before as the Umbral Thief of Fortifying were unleashed by The Devil of Silencing.
Curiously enough, now that I look at it, some of the demons actually are worshippers of Dwarven Gods.
Uklar Yelloozes the Pulp of Larvae, Vomit Monster, is a 93% worshipper of the Dwarven Goddess of Fortresses.
Confusedwitch the Unholy, Monkey Brute, is a 93% worshipper of Arban, Dwarven Goddess of Oaths and Salt.
Sath Ghosturns the Fatal, Panda Fiend, is a 93% worshipper of Sulysoldiers the Whispy, Dwarven Goddess of the Night.
etc.
Unleashed from the underworld to discover religion.
For all of the Hell breaching, this world has a fairly similar goblin population to most other Medium regions I've generated:
20962 Dwarves
90000 Humans
35131 Elves
230659 Goblins
816 Kobolds
Although, that's about 10-15k more Dwarves than I've been generally been getting.