Tropical Forest is the third stage of R-Type Leo. It takes place in some kind of underground rainforest-like swamp. Many plant-like enemies are encountered here.

Trivia[]
Most enemies here are partially organic, probably implying that they are indeed Bydo, though this is just speculation.
This stage was also featured as Mission 17 of the Bydo Campaign of R-Type Tactics II: Operation Bitter Chocolate, with a few enemies returning from R-Type Leo.