Halp w/ OU team

Question

This team is garbage. I'll say that right now.

Diancie @ Diancite
Ability: Clear Body
EVs: 32 Atk / 224 SpA / 252 Spe
Naive Nature
- Diamond Storm
- Moonblast
- Earth Power
- Protect

Heatran @ Leftovers
Ability: Flash Fire
EVs: 248 HP / 220 SpD / 40 Spe
Calm Nature
- Lava Plume
- Toxic
- Roar
- Stealth Rock

Talonflame @ Sharp Beak
Ability: Gale Wings
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Brave Bird
- Flare Blitz
- Swords Dance
- Roost

Rotom-Wash @ Leftovers
Ability: Levitate
EVs: 248 HP / 252 Def / 8 Spe
Bold Nature
- Volt Switch
- Hydro Pump
- Will-O-Wisp
- Pain Split

Magnezone @ Choice Specs
Ability: Magnet Pull
EVs: 172 HP / 252 SpA / 84 SpD
Modest Nature
- Hidden Power [Fire]
- Thunderbolt
- Volt Switch
- Flash Cannon

Latios @ Life Orb
Ability: Levitate
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Defog
- Draco Meteor
- Psyshock
- Roost

Answer 1

Super weak to choice Keldeo. I'd recommend a Serperior over Heatran because it provides the necessary coverage you need on this team while Heatran isn't really needed. You have Diancie, Latios, and Talonflame to deal with Zard Y as well as other things he checks.

Serperior @ Life Orb
Ability: Contrary
EVs: 4 HP / 252 SpAtk / 252 Speed
Timid Nature
- Leaf Storm
- Giga Drain
- Hidden Power [Ground]
- Substitute / Dragon Pulse

Dragon Pulse let's you take care of Dragon types obviously but you already have a slayer in Diancie and Latios. Hidden Power Ground is meant for Heatran as it's a common switch into Serperior. Ferrothorn and Skarmory are also common switch ins but they're both trapped and killed by Magnezone. This also gives you a soft check to Keldeo assuming he's choiced. You can come in after a Scald or Hydro Pump kill and set up a Substitute. Leaf Storm also straight OHKO's. This gives you something to deal with Rotom-W and Lando-T bar Scarf.