My votes:
1. Happy Meal
2. ACME Anvil
3. Kryptonite (It was one of ideas and I'm happy about it)
I'm going with something weirder...
Space Invaders (Square Enix/Taito)
I know I know It's very weird submission, but hear me out.
Who are these guys?
Space Invaders are Enemies, who descend down on Earth and they attack the player with pellets from their mouths and the player needs to shoot at the with Cannon in order to defeat them before they touch the ground and GAME OVER.
Their game was made in 1978 by Japanese video game company Taito, which it was acquired by Square-Enix back in 2005.
Space Invaders are one of greatest video game icons and they are considered as one of important characters to the gaming. Even the crab is Pop-Cultural icon that represents video games, especially the early ones that debuted in 70's and early 80's.
How they could work in Pop Cultural platform Fighter?
Okay, I know some of you argue that Space Invaders can fit as assists or stage Hazards, but they have moveset potential, like they could allude to different Taito games like Duck Hunt alludes to NES Zapper games. They also could have original Moves like they could attack with their tentacles or something like that. Their super moves would be very creative like basically game of Arkanoid or maybe alien Invasion descending down to terrorize the stage.
They could be Trio fighters (Like Ice Climbers, but with third member) and they are not depicted as Voxels, but rather modernized that they resemble our real animals (Crab enemy looks like Crab for example), but they still are aliens from outer space.
Why Space Invaders?
I submit them, because they could represent the early Era of video games and he could be arcade representants that would join the roster. Also they could be wild/weird choice for the roster, but it doesn't mean that they can't join roster, since they are important to video game culture.
Space Invaders is also one most influential sci-fi games and without them we wouldn't see Shoot em up games, which they were also important for game industry.