Arceus-Normal @ Silk Scarf
Ability: Multitype
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Adamant/ Jolly
Swords Dance
Extreme Speed
Shadow Claw
Recover
There's really no point in giving Arceus a Custap Berry, since its base speed of 120 will move before most things anyway; Custap Berry is for Pokemon like Forretress. Also, Extreme Speed is priority, which means Custap Berry is useless. Give it Recover to replenish health, and Arceus really only needs 2 moves to be able to hit everything neutrally.
Deoxys-Attack @ Focus Sash
Ability: Pressure
EVs: 252 Sp. Atk, 252 Speed, 4 Atk
Nature: Mild
Psycho Boost
Superpower
Shadow Ball
Extreme Speed
Mixed attacked; invest EVs in Sp. Atk because Psycho Boost will lower it. Standard Deoxys-A set, not much to say.
Rayquaza @ Life Orb
Ability: Air Lock
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Jolly
Dragon Dance
Outrage
Extreme Speed
V-Create
Dragon Dance > Swords Dance because of the speed boost that V-Create will deduct form. White Herb is a one use item, so it's best to use Life Orb instead for maximum sweeping. Rayquaza won't last long on the battlefield due to its x4 Ice Weakness along with mediocre defences, so you need to maximise its utility before it faints.
Genesect @ Choice Scarf
Ability: Download
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Timid
U-Turn
Ice Beam
Bug Buzz
Flame Thrower
Choice Scarf > Choice Specs; Genesect needs to be fast enough to scout & U-Turn out, or it will take a hit. Its Sp. Atk is high enough without a Spec Boost, but its speed is lacking at a base of 99.
Reshiram @ Leftovers
Ability: Turboblaze
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Timid
Flame Charge
Roost
Dragon Pulse
Blue Flare
Why does Reshiram not have an item on your list? Anyway, some people will recommend Scarf Reshiram, and while that's viable, I personally like a Flame Charge set so you don't get locked into one move. Also, no Draco Meteor because you forfeit your special attack stat. You could go for it if you wanted to, but eh, Dragon Pulse is good enough.
(Therian but there's no sprite for that so...)
Tornadus-T @ Life Orb
Ability: Regenerator
EVs: 252 Speed, 252 Sp. Atk, 4 Atk
Nature: Timid
Hurricane
Grass Knot/ Heat Wave
Focus Blast/ Superpower
U-Turn
Eh... imo Tornadus-T is most worthwhile on rain teams, due to 100% accuracy with Hurricane. I just feel that 70% is more than liable to cost you the game.
Like it was pointed out, you have a Stealth Rock weakness on 3 of your 6 Pokemon and no rapid spinner. Your team is completely on the offensive side, and it's fine if that's what you planned for it, but note that switching is a costly action for you. You have no walls to stall/ take hits, no cleric for team support, and no team support whatsoever. This is essentially a list of 6 Pokemon with ridiculously high stats working on their own.
Forretress @ Leftovers
Ability: Sturdy
EVs: 252 HP, 252 Sp. Def, 4 Def
Nature: Careful
Rapid Spin
Volt Switch
Spikes
Toxic Spikes
Forretress will do well as a rapid spinner, though it's susceptible to Magnezone's Magnet Pull & will be OHKO'd with a HP Fire, though the opponent might set up substitute before using HP Fire, so there's a ray of hope you can escape with Volt Switch.
Excadrill @ Leftovers
Ability: Mold Breaker
EVs: 180 HP, 76 Speed, 252 Sp. Def
Nature: Adamant
Rapid Spin
Earthquake
Rock Slide
Swords Dance/ Substitute
With a few common weaknesses, Excadrill makes up for it by doubling as an attacker, which Forretress cannot fulfil. Mold Breaker is there to hit Levitate types like Gengar and Latio/as, and Rock Slide to deal with flying types.
I suggest replacing your Tornadus with a Rapid Spinner; like I said, I feel as if it's only worthwhile on rain teams due to the low accuracy of Hurricane.
