The Dwarfmule
Most conventional beasts of burden don't take kindly to living in the remnants of the Underempire. Mules are better than most, but even then they oft use more oxygen than can be afforded. Because of this, Dwarves have obtained their own beasts, ones more properly adapted to subterranean life.
The Dwarfmule is, in reality, not a mule at all. They are a type of mobile thermophagic fungus which has evolved to chase lava flows. The dwarves are able to guide this fungus by keeping a hot stone on a rod in front of it, as on might a carrot before a donkey. There are several strains of this fungus bred for speed, endurance, strength, or any other trait a pack animal might normally be bred for.
Dwarfmules do poorly above-ground. The sun's natural heat blinds them during the day, and while they remain usable at night, few merchants are willing to render themselves nocturnal.
Stats
HD:2 AC:13 Atk:+1 Dmg:1d6 Shk:1/13 Mv:30’ Ml:8 Skl:+1 Save:14+