The Donut Plains is a location from Super Mario World. A part of Donut Plains is seen in Episode 3, but otherwise it does not appear in Super Mario Bros. Z, however it is mentioned by Professor E. Gadd in Episode 4.
A screenshot of the actual level in the game compared to Sonic doing the same level in SMBZ.
Nothing is known about the location, other than that Mecha Sonic was searching for a Chaos Emerald there. Considering the robot's ability to sense the Emeralds, it is likely one is there.
Trivia
- The Donut Plains first appeared in Dinosaur Land in Super Mario World, that would mean that the Donut Plains are considered to be in the middle of Cheep Cheep Ocean. However, this could've been an error when Alvin-Earthworm made Episode 3.