I don't think it will have any air, or any metal in it. nor fire nor plant.
Just water lightning earth and cold.
The other possibilities would be ice and crystal or ice and quake. Crystal was used in emerald so odds are they won't use it again so quick. storm and mud was my earlier guess
So I'm going to go with
Ice and quake
Storm and mud
Eta but if I had to pick one I'd stick with my first guess storm and mud
Could also be mountain plasma
But I dont think so