Mega evolution for me it's one of the best additions sadly it's most likely never coming back

Low key? For all the dunking XY has and although the games were clearly unfinished, it had the most accessible and intuitive competative scene

I absolutely loved Roaming on a latios in Pokemon Omega Ruby, i honestly wished that fly just worked like that. Besides that i think triple and rotating battles should be a default type of battle like double battles.

I really enjoyed the Poffin making game in DP, it was pretty satisfying, as well as doing the contests, especially in ORAS. Pokemon Amie was one of my favorites as well, it's cute to see some guests coming over too. One I genuinely hope returns soon is the Dream World, maybe add some improvements and we're good!

Mega Evolution.

Quite literally, the greatest mechanic in the entire franchise, and I wish it was expanded on more. There were so many Pokemon that should've gotten mega-evolved forms. It's partly why I turn to fangames nowadays since they expand on said mechanic by giving certain Pokemon what they've deserved.

I really, really loved Mega Evo. I think as far as gimmicks go it was most likely the easiest and creative one they had. As well as a great springboard to further enhance already great designs. They altered types and abilities, and every game they could have just added more or cycled Megas to shake up the competitive meta.

Also, Pokeball seals. Where you could customize their appearance, I don't see why that ever got removed after being added, it was such a nice touch of personality.