Mega Man Legends 3: Prototype Version is, as the name implies, an incomplete prototype of Mega Man Legends 3 Project. It was intended to be among the first wave of 3DS downloadable titles to launch when the 3DS eShop went live in June of 2011. The purpose behind the prototype was to convince Capcom to continue development on the full game by measuring the response to an incomplete version.
The prototype would have allowed access to a debug menu to allow players to tinker with various game attributes. It was never made clear how much of the full game would be playable, given that the prototype was incomplete code.
On July 18, 2011, Capcom announced via blog that the prototype's release, initially delayed beyond the launch of the 3DS eShop, had been cancelled, as had the full version of the game.