Wobbuffet, anyone? Without Wobb support, Terrakion is going to find it pretty hard to set up. Deoxys-A is going to find it pretty hard to switch in, too.
that, and some sort of defensive arceus, grass, steel, or ghost; provides a solid backbone to a multitude of threats such as ekiller, kyogre, and can spinblock whilst maintaining decent offensive pressure.
I've been saying RestTalk Kyogre the whole time, and continue my support for it. With Deoxys-A and Terrakion around, Chansey and Dialga simply have no chance of walling it.
I'm also liking support Dialga, but why more Speed for lead Groudon? I have never seen a non-Sweeper set running more than 4 EVs in Speed. Come to think of it, I've also never seen a support Dialga running more than 4 EVs either.
if we're using resttalk kyogre (which i'm an advocate of), this looks to me like it's going to be a pretty balanced team; now, i'd either recommend
Support Dialga
Dialga @ Leftovers
Trait: Pressure
EVs: 252 Hp / 92 SpA / 140 SpD / 24 Spe (Can be tweaked, more speed for lead groudon; more SpA for or whatever) IIirc these are just taken from drown all
Stealth Rock
Roar / Dragon Tail / Thunder(my personal preference is roar)
Dragon Pulse
Fire Blast (f u ferro, also lets you 2hko lead 0 SpD groudon)