I am trying to add a last pokemon to this and make improvements, constructive criticism appreciated

Question

Deoxys-Speed @ Leftovers
Ability: Contrary
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
- Draco Meteor
- V-create
- Sunsteel Strike
- Spectral Thief

Blissey (F) @ Leftovers
Ability: Imposter
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
IVs: 0 Atk
- Haze

Buzzwole @ Leftovers
Ability: Triage
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
- Belly Drum
- Drain Punch
- Leech Life
- Photon Geyser

Gengar-Mega @ Spooky Plate
Ability: Normalize
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
- Entrainment
- Quiver Dance
- Boomburst
- Judgment

Rayquaza-Mega @ Leftovers
Ability: Magic Guard
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
- Tail Glow
- Oblivion Wing
- Spectral Thief
- Moongeist Beam

Comments

I assume this is balanced Hackmons. What natures do your Pokémon have? :P

Gengar doesn't need Judgement and should probably have Parting Shot instead. Also, a Black Sludge would suit Gengar better despite the advantage of Spooky Plate. :P

You put Sunsteel Strike on way too many Pokémon. Steel is a bad offensive typing, and Moongiest Beam and Photon Geyser are available, so you should use them. :P

Buzzwole is unviable and outclassed by a lot of other Pokémon in BH. Don't use Buzzwole. :P

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I used judgement for ghost types and impostor

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Leftovers Blissey is almost always worse than Eviolite Chansey. Either way, moves like whirlwind, metal burst, final gambit, and shore up are better than haze.

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Use this

Solagaleo@ Life Orb
Nature: Jolly
Ability: Full Metal Body
EVs 4 hp/ 252 Attack/252 Speed
MOVESET:
Sunsteal Strike (STAB move)
Zen-Headbutt (STAB)
Flare blitz
Earthquake
 
I hope you find this useful.

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I would go a defensive u-turn solgaleo for your team, but it's really your choice.

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Get a pure electric type with wonder guard and magnet rise then come talk to me

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Have you tried that? If yes, can you show us a replay?