Ah ok...well one I’d suggest that might be easier is either...like stated before monotype. Since it is just using one type of pokemon like only using grass type pokemon or bug. Another might be a random pokemon challenge where you randomize your team. So essentially like on pokemon showdown and the random battles.
Some can be, but others are like you play through the game with some rules...Say monotype where you can only use one type or monocolor and only use a certain color of pokemon.
It would depend on the challenge. Cause some might be more detailed with requirements and all that while others are just loose and you can do whatever as long as it fits. So it is more of what you'd be interested in. But in my opinion they are fun just depends on what game and how difficult the challenge might be to "set up".