Fiendwurm

In the Dungeons & Dragons fantasy role-playing game, the Fiendwurm is a magical beast. They have portals to the Abyss (Dungeons & Dragons) in their bellies.

Fiendwurms are the result of an ordinary earthworm having demonic magic cast upon it. In addition to greatly altering and mutating their physical form, this also creates the portal to the Abyss mentioned above in their stomach. This such portal causes them enormous pain, and the only way to relive this is by eating. Because of this the Fiendwurm has a violent nature and attempts to swallow any creature it encounters, and unfortunately, as one might expect, anything swallowed by it goes straight to the Abyss, in other words, Hell!

Physical Description
Fiendwurms resemble enormous (5 feet wide and 80 feet long, the size of the average Purple Worm or Frost Worm) worms. Unlike the earthworms they supposedly once were, they have clearly discernible heads, eyes and mouths. They also have a set of horns and a few spikes around the mouth, and in all honesty their heads are more dragon-like than worm-like. Their tongues are long, purple and forked. Fiendwurms are purple on the topside and blood-pinkish on the underbelly.

Fiendwurms can be found in deserts and plains, and underground.

They are chaotic evil in alignment.

Creative Origins
D&D designer and developer Ed Bonny humorously claims to have imagined the Fiendwurm while eating dinner in Manhattan with friends. Supposedly the idea it just struck him while eating, and he scrawled the concept on paper tablecloth, and it eventually blossomed into the Fiendwurm.

Fiendwurms appeared in the 3rd edition Monster Manual II, and are widely regarded as the nastiest and most maccabre, as well as the most popular creature in the book.