ive wanted to see something like this in halo for a while. could be a silver skull, called like mirror or reflection or something similar. essentially it flips the entire gameworld (ie campaign and other appropriate modes) on the horizontal axis. this may sound silly and trivial, but if you hhave EVER played this mode on uncharted or a more niche gae, king kong, youll know how amazing it is. it’s like playing a whole new game and adds a lot of replay-ability to the campaign
That’d be awesome to see implemented, but it’d be difficult for 343i to make.
Ever played twilight princess on GameCube, then try the Wii version! Boom! I think you have a great idea!