Pike Queen Lucy in Emerald. It was down to my Milotic vs her Milotic, and they had the same moves except that hers had Mirror Coat where mine had Hydro Pump. Therefore, I was going to lose due to running out of PP first. Fortunately my Milotic was frozen by Ice Beam several times, and I made some damn good guesses about when she was going to use Mirror Coat and used it to switch between my Milotic and Armaldo (who was low on HP and eventually died from a stray attack). It was a great moment when hers finally used Struggle first!