Not sure if this has been done before, what about themed triplets for a challenge? For example, you get to choose 3 pokemon, but they might have to behave in a similar way, or look similar. Few examples that come to mind could be say.. Rhydon, Tyranitar and Aggron, or Kabutops, Scyther and Scizor. The triplets have similar abilities and behave similarly, but there's still a good mix for move sets. Not sure if this would add a challenge, but it seems different to all the monotype teams or solo challenges, could be worth a try.