Legacy Information
In "Prototype 2", the exact differences are unknown. However, you cannot play the game, as after the level selection, it only loads up some sprites and information(see photo above.) It is likely a very early release and was used for testing the sprites and player selection.
Note the misspelling is "Lightning" on the cartridge.
The diff of the hexdump's of the retail and "Prototype 2" version can be found here: https://internot.info/docs/thunder.diff