I think our sixth member needs to be Rayquaza. A staple on weatherless teams, Rayquaza gives us a way around weather sweepers while giving us strong priority and a win condition. I used Dragon Claw > Outrage because Rayquaza is still relatively slow and being locked onto Outrage just begs for Rayquaza to be revenge killed. With Dragon Claw, Rayquaza can deal heavy damage while maintaining versatility (such as using ExtremeSpeed to pick off whatever Dragon Claw weakens). Deoxys-S, Latios, Terrakion, and Darkrai are rougly still the same, but seeing as Darkrai can cover opposing Arceus-Ghosts, I've put Arceus-Ghost > Dialga, so we have a spinblocker, another Arceus-Normal check, something immune to Fighting-type moves, and another powerful sweeper / win condition. Arceus-Ghost is also immune to Fighting-type moves, which can be an issue. I decided we needed a bulkier spread on Arceus Ghost, so I went with 252 HP / 4 SpA / 252 Spe so we have something to tank scarfed Dragons and set up. I editted Terrakion's set so now it has Sleep Talk > Toxic, as we now have enough wallbreakers on this team, and things like Lugia and Ho-oh that Toxic would hit can be dealt with through Arceus-Ghost and Rayquaza / Latios, respectively. I also decided to change up the Darkrai set, making it a dual status Darkrai, as I believe that the Paralysis that Darkrai can inflict will be critical in helping facilitate a successful sweep by Latios / Arceus-Ghost. Focus Blast > Nasty Plot and Thunder Wave > Substitute were the changes here.
Rayquaza @ Life Orb
Trait: Air Lock
EVs: 252 Atk / 4 SDef / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Swords Dance
- Dragon Claw
- V-create
- ExtremeSpeed
Arceus-Ghost @ Spooky Plate
Trait: Multitype
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Calm Mind
- Judgment
- Focus Blast
- Recover
Latios (M) @ Soul Dew
Trait: Levitate
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Draco Meteor
- Psyshock
- Grass Knot
- Hidden Power [Fire]
Deoxys-S @ Focus Sash
Trait: Pressure
EVs: 252 Atk / 4 Def / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Stealth Rock
- Spikes
- Taunt
- Fire Punch
Terrakion @ Choice Scarf
Trait: Justified
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Close Combat
- Stone Edge
- X-Scissor
- Sleep Talk
Darkrai @ Life Orb
Trait: Bad Dreams
EVs: 4 Def / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Dark Void
- Thunder Wave
- Dark Pulse
- Focus Blast