[verbatim]

The core of your team is almost identical to mine (Soul Dew Latios, Deo-S, Copyphaze Giratina, Blissey) and I've been doing fairly well. The two biggest threats to this team core, namely, Prankster Groundon and Imposter Blissey. You can cover opposing Blissey by changing up your Latios set and running Escavelier in the space where your Reshiram currently is,

Latios (M) @ Soul Dew
Trait: Magic Bounce
EVs: 252 HP / 252 Atk / 252 Def / 252 SAtk / 252 SDef / 252 Spe
Timid Nature
- Quiver Dance
- Spacial Rend
- Stored Power
- Aura Sphere


Escavalier (M) @ Leftovers
Trait: Prankster
EVs: 252 HP / 252 Atk / 252 Def / 252 SAtk / 252 SDef / 0 Spe
Brave Nature
IVs: 0 Spd
- Copycat
- Gyro Ball
- Destiny Bond
- Rapid Spin

With this combination, Latios is still capable of wrecking after one turn of set up, but once he dies to Blissey (which may not even happen, as Soul Dew Latios will win against Blissey if there both at +1 Spa / +1 SpD / + 1 Spe) you will have a sure fire counter to Blissey, as Escavelier will take miniscule damage so long as you make sure not to overboost Latios before killing Blissey. Escavlier can also make great bait for Contrary V-Create users with Prankster Destiny Bond.