Have you played Pokémon Glazed? If you haven't, play the modified Blazed Glazed instead, a lot of issues with vanilla Glazed are fixed in it, such as the level curve, along with a couple of new features, despite not having some other things that were added onto vanilla Glazed after Blazed was made (it was only like 2 or so things that aren't really too important, probably Mega Evolutions aside from Mega Lucario? But it's still fun and a very good game even without Megas aside from Lucario.). It's one of, if not the best ROM Hacks out there, and it's completed, with 3 entire regions. You even get to choose from 5 starters at the beginning.
Other than that, Pokémon Insurgence is a great fan game. Remember Delta Species from the TCG back in the 3rd generation? (Basically Pokémon with a completely different type than usual.) The main focus of this game are Delta Pokémon, new moves and abilities, evil cults that worship legendaries as the main villains, and new Mega Evolutions, along with a Hardcore difficulty if you want a true challenge (it's still kinda harder than regular Pokémon games anyways on Normal and the story gets really dark and interesting). You'll see stuff like Psychic/Fairy Venusaur, Ghost/Dragon Charizard, and Dark/Fighting Blastoise among other Delta Species. There's also Mega Flygon, Mega Johto starters, and Mega Eevee just to name a few Megas.