What level of clan boss are you on? You have the champions for nightmare/ultra-nightmare. Personally I'd be looking for a speed champ, High Katun is a good one. If for whatever reason you don't want to use her aura then Apothecary is a better choice. High Katun + Apothecary can be used together to make a 2:1 team which seems like it would be really great with Skullcrusher bringing the counter attack