Now that you mention it, I don't think I've utterly conquered any Pokémon game, but I have a few candidates: - Silver: The first and almost onlky time I got a Pokémon up to level 100 without help from any daycare etc, as well as demolishing the E4 several times. - Sapphire: Most total play time probably, and I think I completed every little sidequest and item get, maybe completed the Pokédex with Ruby friends. - Ultra Sun: I'm still not done with it, but since this is the first Pokémon game I've beaten that wasn't one of the first two of a generation (thereby having more postgame), I've done quite a bit of its postgame. I've climbed pretty high up the Battle Tree, I've made huge strides in my breeding, I've caught most of the optional legendaries. Still more to do, but this might be the most for me.
Pokémon Sun. It was the first game where I completed it and filled the Pokédex to get the shiny charm.
Hmm probably Alpha Sapphire. I completed the dex, bred many of my favorites with 5-6IVs and trained them up, played the heck out of super-secret bases, maxed out contests, and generally explored every nook and cranny of the game. I love and miss it so much. Another contender would be DPPt...if I didn't start using Action Replay towards the end to complete my dex since I had no Wi-Fi at the time. orz not exactly a self-achievement
Wow, everyone is much more accomplished than I am. The game I got the furthest in would have to be Pokémon White. I didn't complete the Pokédex but I did get close. First and only (except ultra moon but still playing that one) game to get a Pokémon to level 100 legitimately. And that's about it. As for side series, I got all of the trainer evolutions and legendary's in Pokémon conquest except for Kotaro.
Crystal. I made the elite4 my punching bag, Red was like a pidgey that made me reach 99999 poke dollars. And I had a team of 6 Pokémon that were level 100. I did grind so much that i wouldn't even use flash, I would just walk towards red in the cave.
I felt like I achieved the most in Pokémon HGSS. I did all the things I could and achieved a lot in regards to the Pokeathlon. It just sucks that I had unknowingly bought a pirated version of the game so I could transfer any Pokémon I had from previous iterations of the games.
Pokémon X. I got every single Pokémon on that game and that was a first for me. It took me an entire week and that was a really annoying week.