This massive creature appears to be a 30-foot long sleek black centipede with a long segmented body and many slender legs. Its huge mandibles are serrated and razor-sharp, and its eyes are multi-faceted. A ring of chitinous bone protects its oversized head.
The favored tactic of the tunnel worm is to lurk beneath the surface of the ground or behind a wall until it senses a creature moving by, whereupon it burrows out to surprise and attack its prey (treat this attack as a charge attack). A tunnel worm that has taken more than half its hit points in damage retreats to its lair unless it is cornered, in which case it fights to the death.
Str 22, Dex 13, Con 22, Int 1, Wis 10, Cha 6
If a tunnel worm grapples an opponent wearing armor, it attempts to chew away the armor with its powerful mandibles. With a successful grapple check it deals double its regular bite damage to the opponent's armor. Creatures not wearing armor are unaffected by this special attack. Armor reduced to 0 hit points is destroyed.