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Meteor Smash (Z-Move)
Can be used by a Pokemon holding Smashium-Z (A z-crystal that is basically red and blue tie-dye with the Smash Bros logo in it), only Useable by pokemon playable in Smash Bros.
A Fighting Type Z-move that can instantly KO an enemy pokemon and has a higher chance with lower health. If it connects, the enemy pokemon is flung off screen and ko'ed as if it was in Smash Bros.
I based the Z-Crystal name on the one that lets Snorlax use Pulvarizing Pancake (Snorlium-Z) Not sure what the Pose would be but I'd imagine it would be something along the lines of the Trainer drawing a circle in the are and forming a cross with their arms, creating the Smash Bros Logo.