Whitney in HGSS marks one of the few times I've resorted to using debuffs to win. Instead of trying to brute force Miltank, I had Quilava and Flaaffy collaborate to lower its stats as much as they could, with Flaaffy paralyzing it with Thunder Wave after forcing Miltank to consume the Lum Berry due to Static, then spamming Growl to soften Miltank's damage output, while I had Quilava spam Leer and Smoke Screen to lower its accuracy and Defense substantially. After Flaaffy and Quilava softened Miltank with a series of debuffs, I sent in Heracross and went for the kill with a single Brick Break.
Also one of the funniest ways I attempted to defeat Clair's Kingdra was with Perish Song Lapras. Lapras is bulky enough to survive repeated hits from Kingdra and I used Perish Song in hopes it would defeat Kingdra instantly. Unfortunately, I discovered the AI knows what Perish Song will do, and just before the turn it would've knocked Kingdra out, Clair switched Kingdra out, fortunately I had already switched Lapras out and this baited one of her Dragonair right into my Gyarados's Ice Fang which resulted in a clean win. I sent Lapras in once more after she sent Kingdra out again and used Perish Song to ensure it would go down in a few turns: I ended up not needing it anyway, though, because Lapras and Gyarados combined with Dragon Rage and a critical hit Ice Beam took it down anyway.
Also one of the funniest ways I attempted to defeat Clair's Kingdra was with Perish Song Lapras. Lapras is bulky enough to survive repeated hits from Kingdra and I used Perish Song in hopes it would defeat Kingdra instantly. Unfortunately, I discovered the AI knows what Perish Song will do, and just before the turn it would've knocked Kingdra out, Clair switched Kingdra out, fortunately I had already switched Lapras out and this baited one of her Dragonair right into my Gyarados's Ice Fang which resulted in a clean win. I sent Lapras in once more after she sent Kingdra out again and used Perish Song to ensure it would go down in a few turns: I ended up not needing it anyway, though, because Lapras and Gyarados combined with Dragon Rage and a critical hit Ice Beam took it down anyway.