well, I sent you a VM, but I guess Poppy outlined my thoughts here didn't he.
Like I said before(and what poppy brought up), SD Arceus is troublesome, as the checks on the team are shaky. A quick fix to this is changing Gira-O's EV Spread to 208 HP / 60 Atk / 188 Def / 24 SAtk / 28 Spd
with a Naughty
nature, as it so you takes a +2 SD Arceus's Shadow Claw even after 2 Stealth Rock switch ins, so you can deal with it easier. You could also try Thunder
> Draco Meteor for Manaphy, since it can be troublesome as well once Ferrothorn goes down, though you should be able to phaze it out w/ Diagla before it becomes a menace.
Also, Darkrai and Mewtwo do pose threats, though its harder to fix those without making a significant change. Like I said before, using a Choice Scarf Heracross
over Tentacruel works, as you have something to check Darkrai, as well as Mewtwo with Megahorn, plus it checks Shaymin-S w/o a Sub up and Rayquaza w/o DD with Stone Edge(yea, its shaky, but it sadly never got Ice Punch). With that, you could try a bulkier Kyorge spread, since your team requires rain to keep Ho-Oh and Reshiram in check. As such, a Sub CM Kyorge with 252 HP / 240 Def / 16 SAtk and Ice Beam
or a Thunder Wave Kyorge
can both work, as one means Kyorge can switch into Ho-Oh easier, and with 101 HP Subs, sets up on Chans + Bliss, as well as Ferrothorns without Power Whip(not much, but some omit the move), making it easier to break down teams with. If you do decide to try it, and you do go for Ice Beam, which you'll need for Shaymin-S and Rayquaza, defensibly use Thunder > Draco on Gira-O, since Kyorge would be walled by other Kyorge and Manaphy. On the other hand, Thunder Wave Kyorge cripples switch in such as Shaymin-S and Palkia, making it easier for Dialga to break it down. Ofc, you can use either set and alter to EVs to your liking, though the team is good as is, just some suggestions really than a rate.
So, in summary:
Scarf Heracross > Tenta
Pros: Revenge killer, Ground-resist(not a bulky one, but one never the less) handles Darkrai and checks Mewtwo, checks Shaymin-S and Quaza(w/o subs or DD anyways) with Stone Edge, along with a few other Pokemon, such as Terrakion, Arceus-Grass, and the Latis to name some
Cons: W/o tenta, you don't really have anything to sponge Special Attacks such as Reshiram's Blue Flares (unless you use defensive Kyorge) and you lose out on Rapid Spin, but as far as Spinning goes, you don't have any Pokemon weak to Stealth Rock, though Toxic Spikes can be a bitch(did I mention you lose YOUR Toxic Spikes as well), so you'll have to play smart so that it doesn't get up too many
Sub CM Kyorge or T-Wave > Scarf
Pros: SubCM with my EV spread gives it bulky 101 HP Subs, meaning you set up on Chans/Bliss and Ferro w/o Power Whip, as well as a Pokemon that can switch into Kyorge easily, plus Kyorge gains way more survivability, meaning that it keeps rain longer, helping out your team, while with T-Wave, you can cripple common Kyorge switch ins, making it easier for the team to deal with later, works even better w/o Tenta, since T-Spikes don't conflict with the team anymore
Cons: Losing a much more powerful revenge killer than Heracross, so you'll have to think about that. Imo, your team will work better with a bulkier revenge killer, though its your team, its up to you
@ Choice Scarf
EVs: 252 Atk / 4 Def / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Close Combat
- Sleep Talk
- Stone Edge
Great team Andrew, really great team.