You need a Flying type! Flying is essential to every team, especially an in game one, as you need Fly.
As you are post game, you can get a Mandibuzz relatively easily. You can catch a Vullaby on Route 23 at Level 47, and at Level 54, it will evolve. You can also catch a low leveled Mandibuzz on Thursdays on Route 4.
You can also use Unfezant, which can be easily found on Route 1.
As it is a Flying type, flying types are everywhere, and you are in Post game, it doesn't really matter who you choose. Choose whichever Pokemon you want.
Btw, if you don't want a Flying type, Zekrom can learn Fly, which would be awesome for traveling around Unova. Also, you should get rid of either Outrage or Thunder Fang for Stone Edge/Rock Slide on Krookodile. You already have a Dragon/Electric type in Zekrom, and don't need both types on another Pokemons moveset.
Hope I could help