I've spent two or three night cycles in dark biomes, both forest and mountains, and I can't get any abyssal mobs to spawn. Are the rates just set very low? I feel like there aren't a ton of normal mobs at all, but there are almost no hostile mobs, especially on abyssal biomes. Playing on Sevtech if that matters.
Yes they are somewhat rare compared to single player. This frequently comes up and it is something that was reported to the mod pack developer without any real solution. This is also why you'll find there are no active fish including sharks in the rivers as they quickly flooded the mob cap in the event that multiple players were online. Your best bet to is to seek out the spawners in the farmworld as these are normally clearly visible dungeons above ground that contain all sorts of fun filled mobs to slay. There are also the traditional vanilla style dungeons that contain single spawners of the more important shadow creatures.
