If you are going for an offensive Giratina, use this:
Giratina @ Haban Berry
Hasty nature
4 Atk / 252 SpA / 252 Spe
Draco Meteor
HP Fire
Shadow Sneak
Aura Sphere
Mewtwo needs something like this...
Mewtwo @ Life Orb
Timid nature
4 HP / 252 SpA / 252 Spe
Calm Mind
Ice Beam
Thunderbolt
Psychic
Infernape makes a great Choice Bander....however it's defenses are frail to be locked in to a move that will otherwise be resisted by something else being switched in.
Infernape @ Choice Band
Jolly nature
252 Atk / 4 SpD / 252 Spe
Flare Blitz
Close Combat
U-turn
Stone Edge
Rhydon is good for Substitute, because of it's low speed, it can do some scouting for threats. You can go for Swords Dance over Megahorn if you wish.
Rhydon @ Leftovers
Adamant nature
212 HP / 122 Atk / 176 Spe
Substitute
Rock Slide
Earthquake
Megahorn
Heatran is a beast of a special attacker. It's a steel type's worst nightmare. Choice Scarf is the set that makes him shine. Heatran reaches a maximum Speed stat of 417 when wielding Choice Scarf, outspeeding all Pokémon in OU bar Ninjask.
Heatran @ Choice Scarf
Naive nature
252 SpA / 4 SpD / 252 Spe
Fire Blast
Earth Power
Dragon Pulse
HP Electric or HP Grass
Don't use special attacks on Floatzel, as his base special attack is a terrible base 85. Use physical attacks instead.
Floatzel @ Life Orb
Adamant nature
232 HP / 252 Atk / 8 Def / 16 Spe
Waterfall
Ice Punch
Return
Rain Dance
I hope this all helps, I didn't come up with these movesets or EV spreads on my own, I got them all off of Smogon. Go there for more options.