With hundreds of Pokémon as well as having a metric crapton of characters, don't be surprised that there will always be a character that fans want to check on their cartridges and release them from their game.
Anime & Manga
- The classic Scrappy from the series is Ritchie, a clone of Ash who has no negative qualities and was introduced just to knock Ash out of his first tournament in the following episode. The writers proceeded to bring him back for a Johto mini-arc and then have two episodes in Chronicles focus on him.
- May's Squirtle made a bad first impression with the entire cheapness surrounding its first contest victory and the hate hasn't stopped since. The show already had a beloved Squirtle, making May's a Replacement Scrappy that was possibly particularly disliked by people who prefer Ash's original team.
- The Spiky-Eared Pichu from Pokémon: Arceus and the Jewel of Life, who due to appearing in HGSS in place of Celebi is looking down two smoking-hot hate barrels at once. Game-wise, her stats are pathetic, she cannot evolve into a more-useful form, her moveset is brutally limited, and she replaced Celebi. In the movie, all she does is act cute and grab a key in a dire situation - something that just about any other 'Mon could have accomplished in the same situation.
- Tobias, who, even among the trainers who eliminate Ash from official tournaments, really stands out in how hated he is. Firstly, he has extremely little buildup before his battle with Ash, only appearing in a few cameos. Then there's how he defeats Ash. He wins 6-2 over Ash, and the only two Pokémon he reveals from his party are Latios and Darkrai, a Legendary and a Mythical Pokémon. It is never revealed how he obtained them when only elite Trainers like Frontier Brains have been seen using them, and he seems to serve no purpose other than to eliminate Ash. Many fans took the entire thing as a huge slap in the face.
- Ash's Pignite also gets a lot of flak for being a recycled Charizard and Infernape. Evolving would have changed this, but no; it went the entire Unova series without evolving again.
- The Mewtwo from Pokémon: Genesect and the Legend Awakened. She is quite unpopular with the fandom for filling a role that many believe could have been filled by the well-loved established Mewtwo character from Pokémon: The First Movie and its sequel, for having a voice and personality that contrast sharply with said original Mewtwo, for having no explanation as to how a second Mewtwo is even possible, and for generally being the Fleeting Demographic Rule personified. Even Miriam Pultro, her English voice actress and One of Us, knew that the role would be controversial.
- The Spiky-Eared Pichu and the Pikachu-Colored Pichu in Pokémon HeartGold and SoulSilver fall under this. Not only does the former replace Celebi in an event, but there's pretty much nothing special about them except for their appearance and odd moveset. The Spiky-Eared Pichu can't evolve and can't be transferred to the fifth generation, meaning there's absolutely no reason to even bother with it. (The Pikachu-colored Pichu is at least a "shiny" Pokémon, which are normally rare in the games, though it is still considered a waste of an event as they are already technically accessible in-game, unlike most event Mons.)
- Cresselia is this in Pokémon Mystery Dungeon: Explorers of Darkness/Time/Sky. Not only do you have to escort her to the end of the dungeon (a frustrating task already with regular Pokémon, and she's a Legendary), but she also has the habit of wandering over lava (Which burns her and ends up wasting your Reviver/Heal Seeds). She's also involved in the final battle against Darkrai, in which she's incapable of doing much of anything to him other than fighting off his Mooks.
- From the same PMD games, we have Chatot. Why? For one thing, he's a Jerkass, and then there's the Perfect Apples incident. To summarize: after Team Skull takes the Perfect Apples during your mission to get them, Chatot berates you and your partner for failing. Instead of taking some time to listen to you and learn what happened, he immediately punishes you for going without dinner and forces you to face the Guildmaster. During that scene, even though Team Skull gives Wigglytuff one of the Perfect Apples to rub salt into your wounds, Chatot rubs the failure in your face the next day, telling you to give up on being included for the expedition.