Two things in Emerald. First, fighting a Lady just outside of Petelburg super early in the game. Get her Pokemon to low health, and she uses a freaking FULL RESTORE. A FULL RESTORE! Because God knows a normal Potion wouldn't have worked at those low levels!
Second, catching Rayquaza before the Elite Four. Hell, I caught it before fighting the last Gym Leader! Having a Lv. 70 Rayquaza at that point in the game makes things REALLY easy!
"Let's just say they're...not okay" - Madara Uchiha