depends on what your weaknesses are.
I don't draw Pokemon but i am an artist. i"m basing my answer off of the pokedex pictures.
I always mix up the swirl direction on Polywag, Poliwrath, and Polywhirl.
If you want to be exact to detail ,I'd say it was Gastly, koffing, Moltres, Altaria, or Groudon.
darkrai and arcus
spiritomb, because it has no weaknesses
By far, they have said Celebi is the hardest/rarest Pokemon to obtain outside of Japan.
Not including the legendaries and special pokemon ( ones that you can only catch once ) feebas is the hardest and rarest pokemon to catch
Beat the pokemon league but they are the hardest to beat in the hole game hope I helpd
I think it is vikings
the hardest Pokemon to find is regigigas you can only get him after finding all the other Pokemon and you can find him in the hippodow temple
Magikarp
latias
The Pokémon Ditto.
A fleeing legendary pokemon
feebas
darkrai and arcus
The easyest Pokemon is scizer and the hardest Pokemon is milotic.
Mesprit & Cresselia (legendary)
spiritomb, because it has no weaknesses
Pokemon Rocks Hardest