A round worm is a type of enemy which will periodically burrow into the ground and pop up in different part of the room. If Isaac is in their line of sight when that happens, it will spit a blood shot in his direction.
Like the Round Worm, the Nightcrawler will burrow into the ground and appear somewhere else. When Isaac is within their line of sight, they will fire four short-range projectiles that spiral outward.
Tube Worms were added in Booster Pack #4.
Like the Round Worm, the Tube Worm will burrow into the ground and appear somewhere else. Upon popping out of the ground, they will fire a long-ranged arcing spray of shots at Isaac, attempting to intercept Isaac's future position based on his movement. Unlike standard Round Worms, they can fire at Isaac even if they do not have line of sight.
Like the Round Worm, the Roundy will burrow into the ground and appear somewhere else. When it surfaces, it releases a small rock wave around it and fires an
Ipecac
Replaces tears with explosive and poisoning projectiles fired in an arc from the mouth. shot towards Isaac.
- If multiple Roundy's surface in the radius of their rock wave, they will kill each other.
Like the Round Worm, the Ulcer will burrow into the ground and appear somewhere else. When it surfaces, if Isaac is within its line of sight, it will spawn a Dart Fly, but after spawning 6 of them, it will start firing a blood shot instead. Ulcers burrow underground at a slightly slower rate than most other Worms, usually making them easier to attack.
- Round Worms are parasitic creatures in real life that can be found inside cats or dogs.
- Nightcrawlers in real life could refer to earthworms, although they don't look similar to the Nightcrawlers from the Binding of Isaac.
Ulcers are a reference to ulcers, breaks in bodily membranes caused by sloughing out of inflamed necrotic tissue.
Tube worms are creatures that live underwater and anchor their tails underground, which may be where the Tube Worm from the Binding of Isaac got its name from. However, they don't resemble real life tube worms.
- If a Tube Worm were to be spawned in a floor other than the Flooded Caves, it will have a more Round Worm-like appearance with white skin.
Round Worm on Isaac's Last Will.
Concept drawn for Round Worm.