So I don't really like running a physical bulky dialga
so Instead of the bulk up set I'm going with
EVs: HP 252 SD 252 DF 4
Aura Sphere/Fire Blast
With Iron defense Dialga hits over 500 defense, after 1 turn of set up.
I feel Aura sphere would work better, as it hits Dialga, darkrai, Arceus, Heatran, Tyranitar harder
I'm not sure what to do with the last slot.