I've tried and tried and tried to defeat him but I just can't. I used almost all of my revival seeds fighting Yveltal (I have a few left). But I do have a variety of wands and seeds (sadly no blast seeds). My Pokemon is Mudkip and my partner is Tepig. I have to wait through that big emotional story thing too and I'm really annoyed. Are there any tricks?
Sadly there is not. I spent most of my day trying when I got to the point in the story and used everything. You just damage then die. Then damage die. It may be tedious but when you see what happens during that battle and after you will be in tears. Bear with it and see what happens. You won't be disappointed.
Keep out of range with tepid to slowly wear down to advance the stage. Use Mudkip to damage in range. The thing that covers the ground will knock you out easy. Just keep moving to not die that much.