3. Mega Evolutions

For a lot of Pokémon fans, Mega Evolutions are the gold standard the series’ battle gimmicks will always be beholden to. These temporary transformations enhanced established Pokémon by letting them temporarily evolve into stronger (often edgier-looking) of themselves. It was evocative of something like Digimon, with Pokémon briefly enhancing their capabilities to rise to the occasion of a fight.
A lot of the Mega forms were cool as shit, and gave Pokémon cool typings on top of a new look. Charizard finally got to be a dragon-type and Mewtwo got to throw hands as a fighting-type. It’s one of the coolest reimaginings of old Pokémon, even if not every new design was that stellar. Imagining Pokémon in a Mega form they never got is still a trend among fandom artists. I’m still bitter about Raichu not getting a Mega Evolution, though.