Pokémon Sapphire: "SambaTime" the Ludicolo. I lost it to Milotic vs. Wallace. I was going to Giga Drain, but I accidentally clicked on Ice Beam... Then he used Ice Beam too, and I got a critical hit from his Ice Beam, which sent him straight to its graveyard in Mt. Pyre.
Pokémon Red Fire: "Kobra" the Arbok. Got killed by a Dugtrio in Diglett's cave. Sand Tomb's freaking damage.
Pokémon Pearl: "Brave Bird" the Staraptor, which, ironically, died using his nickname as an attack, Brave Bird. Oh well, at least he took out Cynthia's last Pokémon, Roserade.
Pokémon Diamond: "Luna", a shiny Luxray, named after a friend's Pokémon. Died trying to fight Dialga. Perished to a critical hit Dragon Claw. Luckily, thought, by that time I decided to box fainted Pokémon. I recycled it for the post-ligue in Pokémon Black.
Pokémon Platinum: "Lighting" the Rotom. Died trying to fight against an Ace Trainer in Route 226.
Pokémon Heart Gold: "Shady" the Haunter, which I was just going to evolve with a friend's help. However, it got wrecked by Bianca's Milktank by using Rollout. Fucking bitch. She killed me three times. Thanks to her, I banned the "no leveling up too much" rule from my Nuzlockes.
Pokémon Soul Silver: "Whipper" the Victreebell. Got TOTALLY RAPED by Silver's Sneasel in Victory Road.
Pokémon Black: "Snake" the Serperior, "Daruma" the Darmanitan, and "Hydra" the Zweilous. Fucking Ghetsis' Hydreigon. Period.
HONORABLE MENTION: "Yang" the Reshiram: Literally raped Ghetsis' team. Killed every single one of Ghetsis' Pokémon, except for Cofagrius. Now THAT'S taking revenge.
Pokémon White: "Frankie" the Simisear. Lost against Clay's Krokorok. Critical hit by Bulldoze. Or should I say Bullshit.
And the newest one, Pokémon White 2: "Samurai" the Samurott. Just one thing to say: I FREAKING HATE GHETSIS' FREAKING HYDREIGON!!!!!!!!.