-Pichu, Cleffa, Igglybuff, Azurill. Pointless baby forms for already weak Pokémon that in some regions you can catch before the first or second gym.
-The whole Wurmple line. Very uninspired Caterpie/Weedle replacement.
-Corphish/Crawdaunt
-Plusle, Minun, Pachirisu, Emolga, Dedenne, Togedemaru, Morpeko: All created just to cash in on the Pikachu fan-service even more.
-The elemental monkey trio. Very uninspired filler.
-Munna, Roggenrola, Timburr, Woobat, Bouffalant, too obvious replacements of their Kanto counterparts.
-Basculin
-Alomomola
-Klang and Vanillish specifically: This lines clearly aren't inspired enough to justify three stages, the middle stages seem like Pokédex fillers.
-Perrserker: I hope having a new regional Meowth in every gen doesn't become a new tradition.
-Cresselia, Shaymin, Keldeo, Diancie, Zeraora, Magearna... and any other legendaries/singular Pokémon that have no plot whatsoever and are basically just created for special events, encouraging pre-orders, and make people watch Pokémon movies.

Favorite rom hacks/fan games: Prism, Gaia, Rising Earth, Bushido, Radical Red.