Battle Spot singles or Battle Spot doubles? Because some Pokemon function better in one format than others (Crobat isn't that good in singles, but it can provide some neat support in doubles). Also, you need EVs for each of your Pokemon, as they're important in competitive play.
VGC:
In doubles, Mawile needs 116 HP/252 Atk/140 Spe to outspeed +Speed Mega Salamence under Tailwind. Use Protect over Swords Dance because you're unlikely to set up Swords Dance given Mawile's low Speed and the general fast pace of doubles. Protect also has excellent utility, from stalling out opposing field conditions to letting a partner take out a troublesome opponent. However, Ferrothorn is worth considering because it can handle opposing Primal Kyogre nicely:
-Power Whip
-Gyro Ball
-Leech Seed
-Protect
Nature: Sassy
EVs: 252 HP/220 Atk/36 SDef
Item: Lum Berry
Ability: Iron Barbs
Mega Salamence is superior to its regular counterpart because the former has the Aerilate ability to make its Normal moves Flying. Flying has solid neutral coverage, even hitting Fairy Pokemon hard. You can get away with two Mega Evolutions in VGC and Battle Spot because you can pick one depending on the matchup:
-Draco Meteor/Tailwind
-Double-Edge
-Hyper Voice
-Protect
Nature: Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Salamencite
Ability: Intimidate
I'm iffy about using Metagross and Mawile/Ferrothorn on the same team, as they have redundant roles in Fairy counters. That, and regular Metagross is overshadowed by Mega Metagross in terms of performance. Consider Cresselia for support purposes:
-Psychic/Ice Beam/Icy Wind
-Helping Hand
-Gravity
-Skill Swap
Nature: Sassy
EVs: 244 HP/108 Def/156 SDef
Item: Sitrus Berry/Mental Herb
Scary Face has little use in general, as despite its Speed control potential, other moves like Tailwind, Trick Room, and Icy Wind are superior. The former two affect the whole team, while the latter also deals damage to both targets. Kyogre has little use for Thunderbolt, as that move is outclassed by Thunder, which is perfectly accurate in rain. Water Spout is a move you need to be cautious about, as it will weaken as Kyogre takes damage:
-Water Spout/Origin Pulse
-Ice Beam
-Thunder/Scald/Origin Pulse
-Protect
Nature: Modest
EVs: 252 HP/180 Def/76 SAtk or 116 HP/140 Def/252 SAtk
Item: Blue Orb
Crobat has the right support movepool to function in doubles. Using an offensive set on it is a waste of time because of its middling offenses and shallow offensive move pool:
-Super Fang
-Tailwind
-Taunt
-Quick Guard
Nature: Timid
EVs: 252 HP/4 Def/252 Spe or 44 HP/236 Def/228 Spe
Item: Lum Berry/Mental Herb
Ability: Inner Focus
As cool as regular Gallade is, I don't think it deserves a spot in VGC teams, as its Mega counterpart outclasses it and its middling Speed in conjunction with its frailty on the physical end makes it easy pickings for faster Pokemon. Machamp is something worth considering over it because it provides Wide Guard support to block spread moves:
-Dynamic Punch
-Knock Off/Stone Edge/Protect
-Ice Punch/Stone Edge/Protect
-Wide Guard
Nature: Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Sitrus Berry/Lum Berry
Ability: No Guard
Even with the above changes, you still have to be careful with Talonflame.
Battle Spot:
I'll assume singles here, as I don't have much experience with BS doubles.
Mawile's set is fine as is; just use 132 HP/252 Atk/124 Spe as the EV spread.
Always use Mega Salamence in formats where it isn't banned; Battle Spot is one of these formats:
-Dragon Dance
-Return/Double-Edge
-Earthquake
-Roost/Fire Blast/Hyper Voice
Nature: Adamant/Jolly/Naughty/Naive
EVs: 252 Atk/4 Def/252 Spe
Item: Salamencite
Ability: Intimidate
or
-Draco Meteor
-Return/Double-Edge
-Fire Blast
-Earthquake/Roost/Hyper Voice
Nature: Naive/Rash
EVs: 4 Atk/252 SAtk/252 Spe
Item: Salamencite
Ability: Intimidate
or
-Substitute
-Toxic
-Return/Double-Edge
-Roost
Nature: Jolly
EVs: 252 HP/4 Atk/252 Spe
Item: Salamencite
Ability: Intimidate
Or you can consider Garchomp for its ability to deal with physical attackers effectively because of Rough Skin:
-Outrage
-Earthquake
-Stealth Rock/Swords Dance
-Dragon Claw/Rock Tomb/Fire Blast
Nature: Jolly/Naive
EVs: 4 HP/252 Atk/252 Spe
Item: Focus Sash/Lum Berry/Rocky Helmet
Ability: Rough Skin
or
-Outrage
-Earthquake
-Dragon Claw/Dual Chop
-Stone Edge/Rock Slide/Fire Fang
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf
or
-Swords Dance
-Outrage
-Earthquake
-Dual Chop/Draco Meteor/Stone Edge/Fire Blast
Nature: Naive/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry
As with VGC, using two Mega Evolutions on the team is feasible. However, Mega Metagross is better than regular Metagross because of its better offensive presence thanks to its higher Speed and Tough Claws. If you don't need to use Mega Mawile in a battle, you can use Aegislash as a backup:
-Shadow Ball
-Shadow Sneak
-Flash Cannon/Sacred Sword
-King's Shield
Nature: Quiet
EVs: 252 HP/252 SAtk/4 SDef
Item: Leftovers/Weakness Policy
or
-Substitute
-Toxic
-Flash Cannon/Shadow Ball
-King's Shield
Nature: Modest/Timid
EVs: 252 HP/252 SAtk/4 SDef (Modest) or 252 HP/4 SAtk/252 Spe (Timid)
Item: Leftovers/Air Balloon
or
-Iron Head/Shadow Claw
-Shadow Sneak
-Sacred Sword
-King's Shield/Swords Dance
Nature: Brave/Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Life Orb/Weakness Policy
Kyogre is banned in Battle Spot. The next best alternatives are Azumarill (which, thankfully, doesn't share weaknesses with Mawile) and Greninja:
Azumarill:
-Waterfall
-Play Rough
-Aqua Jet
-Knock Off/Superpower
Nature: Adamant
EVs: 228 HP/252 Atk/12 Def/12 SDef/4 Spe or 164 HP/252 Atk/92 Spe
Item: Lum Berry/Assault Vest
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Superpower/Knock Off/Waterfall
Nature: Adamant
EVs: 228 HP/252 Atk/12 Def/12 SDef/4 Spe or 164 HP/252 Atk/92 Spe
Item: Sitrus Berry
Ability: Huge Power
Greninja:
-Hydro Pump/Water Shuriken/Low Kick/Grass Knot
-Dark Pulse
-Ice Beam
-Gunk Shot
Nature: Naive
EVs: 20 Atk/236 SAtk/252 Spe
Item: Life Orb
Ability: Protean
or
-Hydro Pump
-Dark Pulse
-Ice Beam
-Grass Knot/Extrasensory/Hidden Power (Fire)/Gunk Shot
Nature: Timid/Naive
EVs: 4 HP/252 SAtk/252 Spe
Item: Focus Sash
Ability: Protean
Crobat has a shallow offensive movepool, which I already touched upon. Gengar is a better alternative because it's stronger and has more coverage options:
-Shadow Ball
-Sludge Bomb
-Focus Blast
-Destiny Bond/Icy Wind
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Focus Sash/Life Orb
If you opted for Garchomp over Mega Salamence, Gengar works as the secondary Mega of the team in order to trap and kill counters:
-Shadow Ball
-Sludge Bomb/Focus Blast
-Focus Blast/Icy Wind/Taunt
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Gengarite
or
-Perish Song
-Protect
-Substitute/Disable
-Taunt/Shadow Ball
Nature: Timid
EVs: 252 HP/4 SAtk/252 Spe
Item: Gengarite
You need to be careful around Talonflame, but Garchomp and Mega Salamence somewhat help against it. That being said, they can't be the only ones to deal with it. Aegislash is kind of shaky, as while it resists Brave Bird, it risks getting hit by Flare Blitz. Once again, Cresselia is a good teammate because it has immense bulk to take repeated Brave Birds:
-Psychic/Lunar Dance
-Ice Beam
-Moonlight
-Thunder Wave/Toxic/Lunar Dance/Trick Room
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
