The one rainbow energy is the only possible lightning energy you can use for ERL and then you need to ssu it otherwise its an easy 2 prizes. maybe go 5 fighting and 2 rainbow? donphan really only needs one energy so rainbows aren't too bad for him.
also from my experience with bts 3 is enough...
Its looking like a belted regice would one shot a donphan but that seems risky. Donphan is going to be probably an autoloss. shedninja is a decent counter to donphan but if you only run 1 it will get taken out pretty easily.
The rainbow energys are a good idea as i have no energy search so it doesn't matter. What about a blaziken FB at that point then? That way i can do decent damage to a dialga and i can leave it on the bench to either stall/ slow down kingdra prime???
The only problem i run into with regice is...