Everything

These massive silver orbs are more than just scaled-up versions of dataphytes; omniphages bear clear marks of having been engineered by an external intellect. Fortunately, omniphages possess the same level of intelligence as their smaller cousins... that is, almost none. And now the bad news: Omniphages are exponentially hungrier. They can eat literally anything. They will eat literally anything, too. Matter, antimatter, thoughts, hopes, dreams, magick, they’re not picky. Casting a spell on one of them has a fair chance of feeding it instead of doing any harm.

Since omniphages have the ability to eat anything, they have absolutely no incentive to leave the Deep Umbra where they were marooned. Sure, the beasties could be lured out. Sure, the inhabitants could finally figure out how to push the omniphages out of their reality. But you shouldn’t hold your breath waiting on those scenarios to happen. On the other hand, if the omniphages ever get loose, you probably ought to hold your breath; they eat air, too. At last count, there were three of these things in existence, but no one has risked going out there to see if they’ve reproduced or eaten each other.