The Twilight Cup has a single species clause, though Muk and Alolan Muk will count as separate.
We did the Boulder Cup with 12 people, which was a bit of a poor turnout considering the size of the local community, but we chalked that up to fairly short notice coupled with a bit of uncertainty about the whole thing. Otherwise, it ran pretty smoothly even though I didn't do particularly well.
Skarmory was present, though only about half the number of participants used him. Checking all the lineups, there were no duplicates used.