Roundies burrow and surface like Round Worms. When they resurface, a small, circular rock wave erupts outward, damaging Isaac and enemies alike. After resurfacing, they'll shoot an IPECAC-like shot at Isaac before burrowing again.
- Like other Round Worm-related enemies, Roundies can't fire a shot if Isaac is far away from them.
- Roundies will get killed easily if their rocks waves hit each other.