>>29283472Easy: Pokemon that are based on and not too different from IRL animals.
These pokemon are often easy-mode because they come with a built-in stereotype that an author may both honor and reverse. This saves on establishment, since you can simply have no establishment and trust that the stereotype will hold until you say otherwise.
Pic related: I was once called on featuring a lot of two things—Psychics and Mareep-line. This amused me especially because my next fic features special doggo and his struggle with and against Psychic-typing and at least one sparkysheep. In the latter case, it's always struck me as the kind of pokemon that has a distinct usefulness in each of its forms, but also one that just isn't good enough to see serious use. It falls into the sweet spot as a pokemon that nobody would feel bad about picking up but also not mind letting go, making it useful in supporting cast roles.
Challenging: Pokemon that are basically anthropomorphic innately. Lucario makes a good example of this because it's human enough to be written like one, such that an author forgets that it's a Pokémon; but its other half, jackal-sorta, isn't familiar enough to really bring a stereotype of its own. Indeed, the lore of its loyalty is borrowed from other more familiar canids. This requires that the pokemon be written very carefully with a focus not on either what features and abilities it shares with humans or how it differs from humans or non-humanoid pokemon, but on how it finds for itself a comfortable place along that spectrum. Doubly so if it's living under domestic conditions.
