10. Ditto
Something of a pet peeve of mine, Ditton isn't a useless pokemon by far. It's actually rather essential if you want to get into the breeding game, since Ditto is something of the Jack Harkness of the pokemon series, being able to breed with most of the pokemon in the game, regardless of gender or type. On the other hand, the fact that it hasn't got much originality strikes me as uninspired from a battle tactics perspective. All it does is transform into the enemy pokemon, copying everything about the enemy except for the HP stat. That way you can use it to create rather powerful tanky pokemon or simply copy an enemy damage-dealer and have it have higher than usual health, but the usability of Ditto as a real pokemon are extremely limited due to how hard it is to use properly. It's a slow pokemon, making it generally go second, probably taking it on the chin before being able to transform. It's got bad defense, so it may not be able to take the hit. It simply transforms into the enemy pokemon, making you basically have an open hand about what you pokemon can do.
On the other hand, there's something to be said about in-depth the rumors about Ditto as a pokemon go – I'm especially intrigued by the fact that Ditto resulted out of failed experiments used to attempt to clone Mew, seeing as both pokemon share both their colour and their shiny palette swap.
