Pokemon Unbound is a gen3 romhack with updated mechanics and pokedex up to gen 7ish. When you start, it gives you 3 different options to make the game more challenging (difficult, expert, and insane). It also gives other options, like level caps for each gym, randomized abilities, and a "scalemons" option where every fully evolved pokemon has 600 base stats. I just recently did a run with scalemons and random abilities at the expert difficulty, and it became a really fun challenge of crafting a different team to beat each gym leader. And since I wasn't doing a nuzlocke, the cost of failure and trying again was very low. Lots of side missions and postgame content too.

This game has somewhat spoiled me, in that I wish every other romhack I play had some of the things Unbound has