As said above Whitney with her cheating Miltank. She kept Stomping my Gastly ;_;. I only beat her by suicide Cursing her with Gastly and waiting it out with a Geodude.
Every time I play through Emerald I always stumble at Winona because of Skarmory stopping my Rock Tomb spam and Altaria being just a pain at that level.
In my most recent play through of Emerald Wattson has been the bane of my existence but that is just because my party has no ground types and he just goes hurr durr Shock Wave and one or two shots my whole party. That'll teach me for trying to play a Swampertless play through.