The engine, properly saying, it's really just the regular rm2k3 engine, but modified to work as a platformer. He created it and i worked on the finer details, improving here and there, translating most of the code to english, as it was originally in german.
There are no external plugins or any of that, it's all internal code within the game. You can check the files and the code with the regular rm2k3 tool. There are some test maps in there, i believe.
If you want to study how it works and use it to make your game, feel free to do it. Just having credit for the both of us would be appreciated.