MechaTyranitar
TRC Boss
EVs and IVs totally changed the game for me. I have not done a play-through in the longest time, but my last one was FireRed and me being the perfectionist I am, EV trained and got decent IVs for my storyline team. Other than their effect on my view of the game I think they are amazing, they add a sort of variety to the game that makes it a lot more interesting and a lot more diverse. We got a glimpse of life without them in the Mystery Dungeon games and the level up process was not as interesting as it was in the other games in my view.