I think that a good new approach to take with a hypothetical Meowth playstyle is having him be a "lightweight survivalist". Meowth (in the anime, at least) is notorious for getting electrocuted, beaten, burned, bruised, and sent flying into the stratosphere every single time he gets into a scrap, and somehow, his level of determination is untouchable. This characteristic, coupled with Meowth's noted slyness and underhanded behavior, could translate into Smash as a fighter that ignores the rules of the game and survives being KO'd in ways that other characters aren't able. For example, letting him cling to walls and ceilings is a cat-like behavior that would allow him to cheat death and crawl his way back to safety from the bottom of a stage. I'm sure there are other ideas that could be implemented. In conjunction with the ability to steal items and effects, I can see Meowth as an underdog fighter (which he is portrayed as in the anime): great in free-for-alls with items on, he can use his small size, sneaky behavior, quick reflexes, and fast speed to fight the opponents in his own way while they're distracted, surviving attacks others can't come back from, and keeping himself a constant annoyance on the field by staying alive for irritatingly long times (despite his weight), and snatching items and effects from players whom may just be trying to attack others.