Porygon2

Porygon2 establishes itself as one of the very few viable omniboost sweepers in the tier because of Z-Conversion, which not only boosts all of Porygon2's stats by one stage but also allows it to change into an Electric-type. This grants Porygon2 valuable resistances to Bullet Punch and Flying-type moves and STAB on its potent coverage. Its BoltBeam coverage also gives it everything it needs to hit top-tier threats like Scizor, Latias, and Hydreigon along with almost everything else in the tier neutrally. Porygon2's Speed after boosting is also passable, letting it outpace Latias, Gengar, and Tornadus. Porygon2 is also able to afford running recovery, which further distinguishes itself from Shaymin. However, Porygon2 can only set up once per match, so it relies on a large amount of team support to chip and remove its checks like Blissey and Mega Steelix so it will be able to clean up the remainder of the opponent's team late-game. Porygon2's Speed after boosting up, while usable, still leaves it outsped by common Choice Scarf users like Krookodile, Hydreigon, and Infernape along with naturally fast Pokemon such as Zeraora and Mega Aerodactyl. This tends to force Porygon2 to waste turns restoring its health in order to prevent itself from being revenge killed, which opens up free turns for the opponent. Porygon2's bulk is also marginally lower than Shaymin's, which, in conjunction to its low Speed before using Z-Conversion, can give Porygon2 a more difficult time setting up.