I'm making a Mega Man fan game with Total//Effect and the hit location system from Celestial Bodies. But there's also a tactical side-scrolling combat grid, including rules for gravity and controlling space with projectiles.
Playtests have been REALLY fun! The changed axis of movement makes every choice to change position just so interesting! You're always sandwiched between one obstacle or another, and picking your spacing becomes a really important choice. The risk/reward dynamic of the combat has felt so much more intense than top-down.