I know I?m late to the party, but I got Japanese with Aquarknight. I know, I was surprised, but Aquarknight is an underrated fighter. I use him for most high level red type opponents. My other go to?s are gemstone dragons, especially Tourmaline, the gem/green/pink combo is very effective. Rhodonite is another good gemstone fighter. For high level pure champs, alternating Diamond and Achilles, using bash then magic (and vice versa) usually does the trick.
In this and past tournaments, I?ve noticed more ultra rare opponents, but I don?t think they are any tougher than super rares or even commons. I?ve been stuck on high level commons just as much. I think it comes down to doing the best colour and type matching in the end.