Personally most grass types work well, though anything with the draining moves will be great. I had a Lilligant with Mega Drain and Swords Dance and she wrought havoc. She didn't have a trait, although the best ones in this case would be: Brawny, Feisty, Perky, Speedy, or Techie. Healthy is okay, but because of Mega Drain the others would give different benefits.
There's also a bunch of water types that can use Aqua Ring; the gift Vaporeon had Hydro Pump and Aqua Ring, so with that combo you can use Aqua Ring at the beginning of each level and it will gradually restore HP. My best example was a Goldeen that had Water Pulse and Aqua Ring.
I haven't seen a Ninjask in the game yet (but then again I'm a n00b and am only rank 17).