Pardon me if I read wrong or something, but I'm really sure that some time ago, SSBM gamers divided in two sides: the ones that said that Metal Mario reflected Yoshi's Island, and other that said it wasn't. To resolve the question, I loaded SSBM on the Dolphin emulator. After getting the Metal Mario trophy there, I used Dolphin's texture dump feature. The result was that the following texture is the one being reflected of of Mario:
So yeah, that pretty much looks like Yoshi's Island to me. Discuss.
So yeah, that pretty much looks like Yoshi's Island to me. Discuss.