Changes in Bold:
Klefki @ Leftovers
Ability: Prankster
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Thunder Wave / Toxic
- Magnet Rise
- Spikes
- Foul Play / Play Rough
I changed the EV spread to make Klefki defensively bulky, as it works well with this moveset: if you are defending against Physical attackers then Foul Play will receive a larger boost. Also, most Ground type Pokemon that you switch into for Magnet Rise will be Physcial attackers. You can switch back to the specially defensive spread if you find the team struggling with Special attackers, however; in this case, use Play Rough over Foul Play. You might also want to switch Thunder Wave with Toxic if you find yourself struggling with Special Defense behemoths like Chansey, since most of this team is specially offensive.
Rotom-Wash @ Leftovers
Ability: Levitate
EVs: 248 HP / 252 Def / 8 SpD
Bold Nature
IVs: 0 Atk
- Hydro Pump
- Volt Switch
- Will-O-Wisp
- Pain Split
This is the standard defensive Rotom-W set; as such, no changes are needed.
Latios @ Life Orb
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Psyshock
- Surf / Recover
- Defog
You said you wanted a huge damage dealer? Latios is the Poke for you. You mentioned something about Specs but Latios has great coverage, so you don't want to Choice-lock yourself into a move. Because of this, Life Orb is the preferred item for a boost. The EV spread makes it as fast as possible and dumps the rest into Special Attack. I added Defog for Stealth Rock because Beedrill and Tornadus are weak to them. You can consider Recover over Surf if you find yourself struggling to keep keep Latios alive for Defog, but this greatly reduces coverage.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 184 SpD / 72 Spe
Nature: Calm
IVs: 0 Atk
- Lava Plume
- Toxic
- Taunt
- Stealth Rock
I chose Taunt over Protect as it is generally more useful and allows you to beat Mega-Sableye.
Beedrill-Mega @ Beedrillite
Ability: Adaptability
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Poison Jab
- U-turn
- Drill Run
- Protect
Beedrill does very poorly defensively; as such it is not worth it to invest in defense. Instead, I invested in Speed as much as possible and dumped the rest into Attack, similar to Latios.
Tornadus-Therian @ Assault Vest
Ability: Regenerator
EVs: 96 HP / 160 SpA / 252 Spe
Hasty Nature
- Hurricane
- Focus Blast
- Knock Off
- U-turn
I substituted Focus Blast for Superpower for the higher damage output. Also, you won't need to invest in mixed EVs so I put the Attack EVs into HP for overall bulk.