It's not so easy. Super Smash Flash 2 is an instance of Adobe Air (since Flash downfall), which is a third party software that already has a Mac version. SSB Crusade is a Windows software built from another Windows software, Game Maker. Afaik Game Maker is just straight unable to export a Mac version. They'll have to find a third party workaround, if it's even possible.
Until then, just use Wine like everybody else.