Think of it: in good biomes only, instead of breaching Hell when you mine into the adamantine pillar, you receive a message: "An unbreakable stone floor has been found by the miners! Once you hit enter, you get the message: Strange music can be heard from the wild! Then angels would proceed to assault your fortress in three waves: first, a wave of ten soldiers and thirty workers, then fifteen soldiers and twenty workers, then finally, the Archangel, riding on some great creature, such as a cave dragon, dragon, hydra, maybe even a magic creature like a gryphon or chimera, the chimera being basically a Forgotten Beast. This would make you have a supply of divine metal weapons, armour, cloth, and maybe even bars, if each assistant carried one bar. This would make it somewhat harder and somewhat easier than fighting demons: an endless supply of demons, some of them rather weak, but stocked full of abilities, versus a finite amount of fleshy, well armoured, talented enemies. Imagine the rage fun! provided by being invaded by angels, when many probably didn't know they existed. Exceptional and master crafted steel could most likely be equal to the divine metals, since my dwarves put a master work bismuth bronze spear over a basic steel spear. But then getting your forges making master crafted divine metal weapons and armour and adamantine, you could probably arm half a large military better than steel. But they'd only attack when biomes are good. I'd imagine this might cause problems in the rare good+evil biomes. Maybe twice the rage fun!? I don't know. I thought of it while fighting some angels in my fortress-made steel arms, being a near equal for a soldier one-on-one. Thanks for reading! Sorry it was so long.