making an interesting single player game is a wholly different task from making an interesting competitive multiplayer game (especially if that competitive multiplayer game features asymmetrical options)
if you want to play a beat 'em up, play one, if you want to play a fighting game (extremely different), play one of those, they're too different to expect them to be reasonably packaged together
i also do not recommend trying to play a fighting game if you have absolutely no one to compete against!! that shouldn't be much of a problem because all the big new fighting games have online play built-in and most of the old ones are supported on kaillera, GGPO, or supercade anyway
if you want to play a beat 'em up, play one, if you want to play a fighting game (extremely different), play one of those, they're too different to expect them to be reasonably packaged together
i also do not recommend trying to play a fighting game if you have absolutely no one to compete against!! that shouldn't be much of a problem because all the big new fighting games have online play built-in and most of the old ones are supported on kaillera, GGPO, or supercade anyway