"Acid Creatures" is a stage in R-Type III: The Third Lightning. Similar to The Cave, it's a place swarming with organic Bydo organisms. Pilots must expect close-quarters combat. In addition to the teeming Bydo lifeforms, a primary hazard is the constant acidic drizzle dropping from the ceiling. This acid will eat through stage elements and R-craft alike. If pilots wait long enough, the acid will melt through objects, making it easier to fly around them.
Another hazard are thick walls of Bydo cells that completely block further progress. These cells are maintained by a single large cell; destroying this "parent" cell will cause the immediate destruction of the entire cell wall. One one occasion, this cell is present on the other side of a cell wall, and attacking it via the Mega Wave Cannon is the only way to proceed.