Help on possible team ORAS

[Captain Nexus]

Skarmory Leftovers (Spikes/stealthrock)
Greninja w protean Life orb(Spa sweeper)
Gengar Gengarite/Lifeorb(Spa sweeper)
Slowbro Leftovers/Slowbroite (Wall)
Mawile Mawilite/Choice ??? (Hp/Attack)
Garchomp Choicescarf (Phys Sweeper)
Tell me what you think! And who should be my mega in this comp? Any overpowering weaknesses? Electric is the only one I can see but I might be overlooking something. Thanks everyone, criticism is always welcome.
**Ive never really played competitive before but it seemed fun so with my knowledge i constructed this team**

 

[PlatinumDude]

I'd replace Skarmory with Ferrothorn, as Ferrothorn provides another Electric resistance:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip/Protect
-Gyro Ball/Thunder Wave
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers/Shed Shell
Ability: Iron Barbs

Mixed Greninja is better this time around:
-Hydro Pump/Low Kick
-Ice Beam
-Gunk Shot
-Dark Pulse/Hidden Power (Fire)/Grass Knot
Nature: Naive
EVs: 40 Atk/216 SAtk/252 Spe
Item: Life Orb
Ability: Protean

or
-Spikes
-Hydro Pump
-Dark Pulse/Ice Beam
-Hidden Power (Grass)/Grass Knot/Dark Pulse
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash
Ability: Protean

Gengarite is banned to Ubers. Regular Gengar is still quite good, really:
-Shadow Ball
-Sludge Wave/Sludge Bomb
-Focus Blast
-Destiny Bond/Taunt/Substitute
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Focus Sash/Black Sludge

or
-Substitute
-Shadow Ball
-Will-o-Wisp
-Taunt/Sludge Bomb/Sludge Wave/Disable
Nature: Timid
EVs: 28 HP/148 SAtk/80 SDef/252 Spe
Item: Black Sludge

or
-Hex
-Taunt
-Will-o-Wisp
-Sludge Wave/Sludge Bomb/Substitute
Nature: Timid
EVs: 8 HP/248 SAtk/252 Spe
Item: Black Sludge

Regular Slowbro and Mega Slowbro are equally viable:
-Scald
-Psyshock/Fire Blast/Ice Beam/Foul Play
-Thunder Wave/Toxic
-Slack Off
Nature: Bold
EVs: 252 HP/232 Def/24 SDef
Item: Leftovers/Slowbronite
Ability: Regenerator

or
-Calm Mind
-Scald
-Rest
-Sleep Talk
Nature: Bold
EVs: 252 HP/232 Def/24 SDef
Item: Slowbronite
Ability: Regenerator

or
-Calm Mind
-Iron Defense
-Scald
-Slack Off
Nature: Bold
EVs: 252 HP/4 Def/252 SDef
Item: Slowbronite
Ability: Regenerator

Mawilite is banned to Ubers. And Mawile is terrible without its Mega Evolution. Magnezone, Heatran and Bisharp are good substitutes over it if you're using Slowbro as your Mega:

Magnezone:
-Thunderbolt
-Volt Switch
-Flash Cannon
-Hidden Power (Fire)
Nature: Modest/Timid
EVs: 172 HP/252 SAtk/84 Spe (Modest) or 4 HP/252 SAtk/252 Spe (Timid)
Item: Choice Specs (Modest)/Choice Scarf (Timid)
Ability: Magnet Pull

or
-Magnet Rise
-Thunderbolt
-Flash Cannon
-Hidden Power (Fire)
Nature: Modest
EVs: 128 HP/252 SAtk/128 Spe
Item: Air Balloon
Ability: Magnet Pull

Heatran:
-Overheat/Fire Blast
-Flash Cannon/Hidden Power (Ice)
-Earth Power/Flamethrower
-Stone Edge/Ancient Power
Nature: Timid/Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Scarf

or
-Stealth Rock
-Fire Blast/Flamethrower
-Flash Cannon/Earth Power/Toxic/Will-o-Wisp
-Taunt
Nature: Timid/Modest
EVs: 12 HP/252 SAtk/244 Spe
Item: Air Balloon

or
-Magma Storm
-Earth Power
-Taunt
-Toxic
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Leftovers/Air Balloon

or
-Lava Plume
-Toxic
-Taunt/Earth Power/Roar
-Stealth Rock/Protect/Earth Power
Nature: Calm
EVs: 248 HP/192 SDef/68 Spe
Item: Leftovers

Bisharp:
-Sucker Punch
-Iron Head
-Knock Off
-Pursuit/Swords Dance
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Dread Plate/Black Glasses
Ability: Defiant

Scarf Garchomp should use:
-Outrage
-Earthquake
-Stone Edge/Fire Blast
-Dragon Claw/Dual Chop
Nature: Jolly/Naive
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Scarf

 

[Captain Nexus]

Thank you very much, I kind of modeled the team around mega gengar, as he is a beast. Would any other pokemon be his equal in special sweeping that you could recommend? Thanks again!

 

[PlatinumDude]

Thank you very much, I kind of modeled the team around mega gengar, as he is a beast. Would any other pokemon be his equal in special sweeping that you could recommend? Thanks again!

Mega Alakazam has similar offensive presence and can potentially pick up useful abilities with Trace:
-Psychic
-Shadow Ball
-Focus Blast/Hidden Power (Fire)
-Taunt/Thunder Wave/Protect
Nature: Timid/Modest
EVs: 4 HP/252 SAtk/252 Spe
Item: Alakazite
Ability: Magic Guard

Mega Gardevoir also works:
-Psyshock
-Hyper Voice
-Focus Blast/Hidden Power (Ground)
-Taunt/Will-o-Wisp/Calm Mind/Substitute
Nature: Timid/Modest
EVs: 24 Def/232 SAtk/252 Spe
Item: Gardevoirite
Ability: Trace

Mega Sceptile is also a good cleaner, thanks to its good Speed:
-Substitute
-Giga Drain
-Dragon Pulse
-Focus Blast
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Sceptilite
Ability: Overgrow

or
-Leaf Storm/Energy Ball
-Dragon Pulse
-Hidden Power (Fire)/Focus Blast
-Earthquake/Protect
Nature: Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Sceptilite
Ability: Overgrow

These Megas are options only if you're not using Slowbro as your Mega.

 

[Captain Nexus]

I think I will use slowbro as my mega, the giant tank is very appealing to me, it seems as if my team will be really weak to fighting types, which is alright. I think Gardevoir will work well in this team

 

[PlatinumDude]

I think I will use slowbro as my mega, the giant tank is very appealing to me, it seems as if my team will be really weak to fighting types, which is alright. I think Gardevoir will work well in this team

Gardevoir is only good in its Mega form; its regular form is mediocre. Non-Mega Fairies to turn to are Azumarill, Sylveon and Clefable:

Azumarill:
-Waterfall
-Aqua Jet
-Play Rough
-Superpower/Knock Off
Nature: Adamant
EVs: 228 HP/252 Atk/28 Spe (Choice Band) or 16 HP/252 Atk/240 SDef (Assault Vest)
Item: Choice Band/Assault Vest
Ability: Huge Power

or
-Belly Drum
-Aqua Jet
-Play Rough
-Waterfall/Superpower
Nature: Adamant
EVs: 92 HP/252 Atk/164 Spe
Item: Sitrus Berry
Ability: Huge Power

Sylveon:
-Wish
-Protect
-Hyper Voice
-Heal Bell
Nature: Bold
EVs: 252 HP/216 Def/40 SDef
Item: Leftovers
Ability: Pixilate

or
-Hyper Voice
-Psyshock
-Shadow Ball
-Baton Pass/Hidden Power (Fire/Ground)
Nature: Modest
EVs: 244 HP/252 SAtk/12 Spe
Item: Choice Specs
Ability: Pixilate

Clefable:
-Calm Mind
-Moonblast
-Stored Power/Flamethrower
-Soft-Boiled/Moonlight
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Life Orb
Ability: Magic Guard

or
-Wish
-Protect
-Moonblast
-Heal Bell/Aromatherapy/Thunder Wave
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Unaware

or
-Moonblast
-Fire Blast
-Thunder Wave
-Soft-Boiled/Moonlight
Nature: Modest
EVs: 252 HP/4 Def/252 SAtk
Item: Life Orb
Ability: Magic Guard

or
-Stealth Rock
-Moonblast
-Fire Blast
-Soft-Boiled/Moonlight
Nature: Calm
EVs: 252 HP/160 Def/96 SDef
Item: Leftovers
Ability: Magic Guard