Do you think Burrowers should be a 'monster type', or should each individual be unique, like demon lords, archdevils, etc.?

I think there's precedent in the Mystara Hollow World material for there being both 'Lesser Burrowers'/Giant Annelids and the real Burrowers. Maybe the first are a standard monster type, and the second are unique individuals of near-Immortal power?

(Personally, my mental image of the Burrowers has always been Brian Lumley's Chthonians -- rock-burrowing/lava-swimming telepathic squid. But they could have a huge variety of forms; I could see basing one on a Star-nosed Mole the size of a whale, there could be some that don't really look like a natural burrowing form but disintegrate their way through rock, etc.)