Meowth is one of the most iconic Pokemon in the franchise for being the main antagonist Pokemon of the anime series as part of Team Rocket.
IMO Meowth is just as iconic as Pokemon like Charizard or Jigglypuff who are also playable in the SSB series and have had notable specimen in the anime (Ash's Charizard, the JIgglypuff that followed Ash and Friends for years).
But Meowth has only been a PokeBall Pokemon (except in Melee) in the Smash series. With a Smash game for the Switch on the horizon (possibly), it's time for Meowth to become the second Pokemon (after Charizard) to make the move from being a PokeBall summon to playable character. The Pokemon anime turns 20 this year, and Meowth (and TR) isn't going away from the show anytime soon that I can hear.