Shit, this team is awesome. Just one question. Is Magnezone really needed on this team? Jirachi handles Scizor, Suicune can roar away a once SDed Scizor in emergencies. and Salamance has Fire Fang/Flamethrower (personally, I prefer Fire Blast as it hits Skarm harder than a +1 Fire Fang).
There is one pokemon that this team has problems against - Infernape. Flamethrower for Magnezone and Jirachi, Close Combat for Blissey, Grass Knot for Suicune, HP Ice for Salamance and Cresselia, after resting, may faint before she wakes up to rest again from repeated Flamethrowers (Nasty Plot means Infernape will always win). Ape can swap in after Magnezone traps and kills a steel, and your best hope is to swap in Suicune to absorb an attack and then a Grass Knot. It takes 46.04-54.46% damage; it will survive, but combine that with the attack that it swapped into and SR damage (minus one turn of Leftovers recovery) and Suicune has lost lots of health; it can only do this if it is sufficiently healthy. And prediction wars by swapping between Blissey to absorb special attacks and Salamance/Suicune for Close Combat is a poor idea, as Infernape has 11 turns (thanks to LO) to predict a Close Combat on Blissey, HP Ice on Salamance e.g., all with SR wearing down your health.
Magnezone should be replaced by Tentacruel, who comfortably walls all of Infernape's attacks, as well as Scizor. The moves I would use are Surf, Ice Beam, Rapid Spin and Knock Off. Rapid Spin's use is obvious, but your team has 4 pokemon vulnerable to Spikes and 2 to Tspikes (Blissey may suffer Aromtherapy PP issues against Stall teams, especially considering Suicune and Cresselia rely on a cleric). Without Magnezone, Skarmory and Forretress may set them up easier, so Tentacruel needs to be around to remove entry hazards (which Mag cannot do). Salamance is your strongest form of offence, and he needs to be kept alive. Knock Off is recommended over Tspikes. Your team places a large dependence on Cress spreading Burn to your opponent's team, and Tyranitar cannot be burnt if he is affected by Tspikes. Blissey also has Toxic should you need it. Knock Off removes your opponent's Leftovers, meaning that your opponent will be unable to stall as easily with a burn. Tentacruel is a great anti-stall team pokemon.