When you roll a 12 on the breeder groups table, or if you just feel like it, you can select (or roll randomly) one of these.

Unless otherwise stated, delvers are of chaotic alignment.

Roll Delving Group
1 Creeper: Whenever a creeper Black-round-md is killed in an encounter, it explodes: carve out a jagged hole, less than a bead in size, at the location of the encounter. (Duncan Timiney)
2 Changelings: Start with 2Black-round-md and 0White-round-md. Whenever the Changelings win an Encounter check, both they and the Monster Group they just encountered gain 1Black-round-md. (Rolfe Bergstrom)
3 Kender: Whenever Kender encounter another Monster Group, they first automatically steal 1White-round-md from that group. Then they roll for the encounter as normal, but with -1 on the Kender's roll. (Rolfe Bergstrom, based on the Kender from Dragonlance)
4 Goblin Herders: At the end of their Season, if they are supported, add a Feral Squig Black-round-md anywhere in their Zone of Control. The Feral Squig Black-round-md is a wandering monster that ignores (and is ignored by) Goblins. (Rolfe Bergstrom, based on the Night Goblins from Warhammer Fantasy and the Orks from Warhammer 40k)