I've been meaning to use the Carpippheleagerabold for something. Let's see what happens.
They have a Minotaur's starting abilities on steroids (made them all Legendary Wrestlers), jacked up mental and physical attributes, and [PRONE_TO_RAGE:100]. To even out the playing field against the countless hordes, I gave them what I hope is demon dissolving blood. It's a combination of Helmet Snake venom and Gnomeblight'e effects with the severity of each part of the syndrome set to 1000, the start to 0 and peak to 1.
Biome is set to SUBTERRANEAN_CHASM:5:5. The entity is named ABYSS and set as Layer_Linked.
Here we go.
Well, the first world gen crashed Dwarf Fortress fifty years in. Let's try that again.
Okay, a small world worked without crashing. Let's see if a bigger one will work.
A Medium sized world managed to get past fifty years this time. I finally had it cancel the world gen history around 165 or so though since it really slowed to a crawl, which only happened around the thirty year mark. Something's definitely going on down there. It took probably two or three times as long as usual to generate that world.
Based on a few world gens, it doesn't seem like creatures generated in the underworld appear in Legends mode unless they escape to the surface. There may be a way around this. Otherwise, there's no way to know if they're thriving down there or not.