Frog World
Frog world is full of textures reminiscent of older videogames, with bright tile flooring and rich brick walls. Frog world doesn't spawn with interior walls, but instead rooms are often filled with boxes that span floor to ceiling and are breakable, these act as pots and drop loot (affected by pot breaking ring buff), as well as pink floor spikes that do no damage but impede movement slightly. Frog World introduces two new enemies, the Worm Servant, and The Experiment. The portal back to one of 3 default floors will appear after defeating the final boss, the Worm Lord.
Frog World starting room
Worm Servant and The Experiment
Access
Frog World is entered through a portal that has a chance to appear in Secret rooms. A community guide refers to its boss fight as "three worms", which matches the Worm Lord achievement. See Achievements.
Community-sourced (added October 2026, not yet verified in-game). Sources: Steam guide: "every achievement guide" (MSK).