Dekayi (CR 2)

Large Animal
Alignment: Always neutral
Initiative: +0; Senses: low-light vision, tremorsense 60 ft., and Listen +5

AC: 12 (-1 size, +3 natural), touch 9, flat-footed 12
Hit Dice: 3d8+12 (25 hp)
Fort +6, Ref +3, Will +1
Speed: 30 ft., burrow 20 ft. (dirt and sand only), swim 20 ft.
Space: 10 ft./5 ft.
Base Attack +2; Grapple +10
Attack: bite +5 melee
Damage: Bite 1d6+4
Special Attacks/Actions:
Abilities: Str 18, Dex 10, Con 17, Int 1, Wis 11, Cha 2
Special Qualities: resistance to poison (+4 vs poison)
Feats: Endurance, Toughness
Skills: Listen +5 and Swim +13
Advancement: 4-14 HD (Large), 15+ HD (Huge)
Climate/Terrain: Underground
Organization: Domesticated
Treasure/Possessions: None

Source: Dragon #345

Also called "mulesnakes," dekayi are common mounts in the dirt tunnels of the shallow Underdark, where they can burrow through sand and dirt (they cannot burrow through stone or other solid materials). A specially shielded saddle allows a rider and his provisions to travel with the dekayi as it burrows.