Megapede (CR 20)

Colossal Vermin
Alignment: Always neutral
Initiative: -2 (Dex); Senses: tremorsense, darkvision 60 ft., Listen +10, and Spot +7

AC: 18 (-8 size, -2 Dex, +18 natural), touch 0, flat-footed 18
Hit Dice: 32d8+256 (400 hp); DR: 15/magic adamantine
Fort +26, Ref +8, Will +11
Speed: 80 ft., burrow 20 ft.
Space: 100 ft./10 ft.
Base Attack +24; Grapple +56
Attack: 5 tentacle rakes +32 melee, or bite +32 melee
Full Attack: 5 tentacle rakes +32 melee, or bite +32 melee
Damage: Tentacle rake 2d8+16, bite 4d6+16 plus poison (DC 34)
Special Attacks/Actions: Poison
Abilities: Str 43, Dex 7, Con 27, Int -, Wis 12, Cha 4
Special Qualities: SR 31, vermin traits
Feats: -
Skills: Listen +10 and Spot +7
Advancement: 33-64 HD (Colossal)
Climate/Terrain: Warm desert
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual II

Poison (Ex): A megapede delivers its poison (Fortitude save DC 44) with each successful bite attack. The initial and secondary damage is the same (2d6 points of Constitution damage and 1d4 points of Dexterity drain).

Tremorsense (Ex): A megapede can automatically sense the location of anything within 120 feet that is in contact with the ground.

Megapedes lie in wait just under the sandy surface of the desert, lunging at creatures who wander too near. In a fight, a megapede usually rends its enemy with five vicious claw attacks per round. It reserves its poisonous bite for foes that prove especially daunting.

True terrors of the desert, megapedes constantly hunt the dunes and sandy plains for food. The desert offers little refuge to creatures fleeing these enormous predators.

A megapede looks like an enormous centipede with a long, segmented body and hundreds of pairs of legs. Its tough, bulbous body is covered with dense orange and brown bristles. The creature's tremendous mandibles twitch involuntarily when it senses prey. A megapede can grow to more than 100 feet in length.