I'll rate this team assuming it's an OU one. Take note that Darkrai and Groudon are Uber Pokemon, meaning they can't be used in OU teams. Also take note you can only Mega Evolve 1 Pokemon per battle, so if I suggest any Mega Evolutions, only pick one.
Eelektross is outclassed by other Electric Pokemon like Raikou, Thundurus, Mega Manectric and Wash Rotom as they're faster and/or have good support options. Eelektross is also rather slow and not too bulky:
Raikou:
-Thunderbolt
-Volt Switch
-Hidden Power (Ice)
-Shadow Ball/Extrasensory
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs/Assault Vest
or
-Calm Mind
-Thunderbolt
-Hidden Power (Ice)
-Extrasensory/Substitute
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Thundurus:
-Thunderbolt
-Hidden Power (Ice)
-Focus Blast/Psychic
-Thunder Wave
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb/Leftovers
Ability: Prankster
or
-Nasty Plot
-Thunderbolt
-Hidden Power (Ice)
-Focus Blast/Thunder Wave/Substitute
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb/Leftovers
Ability: Prankster
or
-Thunderbolt
-Hidden Power (Ice)
-Knock Off
-Superpower/Thunder Wave
Nature: Naive
EVs: 76 Atk/180 SAtk/252 Spe
Item: Life Orb
Manectric:
-Thunderbolt
-Volt Switch
-Overheat
-Hidden Power (Ice)
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Manectite
Ability: Lightning Rod
Wash Rotom:
-Volt Switch
-Hydro Pump
-Will-o-Wisp
-Pain Split/Rest
Nature: Bold/Calm
EVs: 248 HP/216 Def/44 Spe (Bold) or 248 HP/216 SDef/44 Spe (Calm)
Item: Leftovers/Chesto Berry
Latios has better coverage options than Fly and Ice Beam. Ice Beam shouldn't be used on Dragons not named Kyurem, as it has redundant coverage with Dragon. Luster Purge is also a very underwhelming signature move; it's weaker than both Psychic and Psyshock:
-Draco Meteor
-Psyshock
-Hidden Power (Fire)/Surf/Earthquake
-Roost/Defog
Nature: Timid/Hasty
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb
or
-Draco Meteor
-Psyshock
-Tailwind/Hidden Power (Fire)/Defog
-Trick
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Choice Scarf
Alternatives to Darkrai are Bisharp, Mandibuzz, Weavile, Mega Absol, Mega Sableye, Mega Houndoom, Mega Gyarados, Tyranitar and Mega Sharpedo:
Bisharp:
-Sucker Punch
-Iron Head
-Knock Off
-Pursuit/Swords Dance
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Black Glasses/Dread Plate/Life Orb/Lum Berry
Ability: Defiant
or
-Sucker Punch
-Iron Head
-Knock Off
-Pursuit
Nature: Adamant
EVs: 192 HP/220 Atk/96 Spe
Item: Assault Vest
Ability: Defiant
Sableye:
-Calm Mind
-Dark Pulse/Snarl/Shadow Ball
-Will-o-Wisp
-Recover
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Sablenite
Ability: Prankster
Mandibuzz:
-Foul Play
-Roost
-Taunt/Whirlwind
-Defog/Toxic/Knock Off
Nature: Bold/Impish
EVs: 248 HP/136 Def/108 SDef/16 Spe
Item: Leftovers
Ability: Overcoat
Weavile:
-Knock Off
-Icicle Crash
-Ice Shard
-Low Kick/Pursuit/Poison Jab
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb
Ability: Pressure
Mega Absol:
-Swords Dance
-Sucker Punch
-Knock Off/Baton Pass
-Play Rough/Baton Pass
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Absolite
or
-Sucker Punch
-Knock Off
-Play Rough/Superpower
-Ice Beam/Fire Blast
Nature: Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Absolite
Mega Houndoom:
-Nasty Plot
-Dark Pulse
-Fire Blast
-Will-o-Wisp/Taunt
Nature: Timid
EVs: 40 HP/8 Def/208 SAtk/252 Spe
Item: Houndoominite
Ability: Flash Fire
Gyarados:
-Dragon Dance
-Waterfall
-Crunch
-Earthquake/Taunt/Substitute
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Gyaradosite
Ability: Intimidate
Tyranitar:
-Stone Edge
-Crunch/Ice Punch
-Pursuit
-Fire Blast/Superpower
Nature: Naive/Jolly
EVs: 252 Atk/4 SAtk/252 Spe
Item: Choice Scarf
Ability: Sand Stream
or
-Stealth Rock
-Rock Slide/Ice Beam/Thunder Wave
-Crunch/Pursuit
-Fire Blast
Nature: Sassy
EVs: 248 HP/136 Def/124 SDef
Item: Leftovers
Ability: Sand Stream
Mega Sharpedo:
-Hydro Pump/Waterfall
-Crunch
-Poison Jab
-Protect
Nature: Naughty/Adamant
EVs: 228 Atk/28 SAtk/252 Spe
Item: Sharpedonite
Ability: Speed Boost
Ground and Fire alternatives to Primal Groudon are Excadrill, Gliscor, Therian Landorus, Talonflame, Heatran, Charizard and even Mega Camerupt:
Excadrill:
-Earthquake
-Iron Head
-Rock Slide
-Rapid Spin
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Air Balloon
Ability: Sand Rush
or
-Earthquake
-Iron Head
-Rock Slide
-Rapid Spin
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf
Ability: Mold Breaker
Gliscor:
-Earthquake
-Substitute/Knock Off
-Toxic
-Protect
Nature: Impish
EVs: 252 HP/184 Def/72 Spe
Item: Toxic Orb
Ability: Poison Heal
or
-Earthquake
-Acrobatics
-Taunt/Toxic/Fling
-Roost
Nature: Impish
EVs: 252 HP/56 Def/200 Spe
Item: Toxic Orb
Ability: Poison Heal
or
-Earthquake/Knock Off
-Toxic/Knock Off
-Taunt
-Roost
Nature: Careful
EVs: 252 HP/184 SDef/72 Spe
Item: Toxic Orb
Ability: Poison Heal
Therian Landorus:
-Stealth Rock
-Earthquake
-U-turn
-Stone Edge/Rock Slide/Knock Off
Nature: Impish
EVs: 252 HP/240 Def/8 SDef/8 Spe
Item: Leftovers
or
-Stealth Rock
-Earthquake
-U-turn/Explosion
-Stone Edge/Smack Down/Knock Off
Nature: Adamant/Jolly
EVs: 72 HP/252 Atk/184 Spe
Item: Soft Sand/Earth Plate/Normal Gem
or
-Earthquake
-U-turn
-Stone Edge/Rock Slide/Knock Off
-Superpower/Explosion
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf
or
-Swords Dance
-Rock Polish
-Earthquake
-Stone Edge
Nature: Jolly/Adamant
EVs: 56 HP/220 Atk/232 Spe
Item: Leftovers/Life Orb/Soft Sand/Earth Plate
Talonflame:
-Swords Dance
-Flare Blitz
-Brave Bird
-Roost
Nature: Jolly
EVs: 88 HP/252 Atk/168 Spe
Item: Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Flare Blitz
-Brave Bird
-U-turn
-Steel Wing/Tailwind
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band
Ability: Gale Wings
or
-Swords Dance
-Brave Bird
-Taunt/Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers
Ability: Gale Wings
Charizard:
-Dragon Dance
-Flare Blitz/Earthquake
-Dragon Claw
-Roost
Nature: Adamant/Jolly
EVs: 96 HP/252 Atk/160 Spe
Item: Charizardite X
Ability: Blaze
or
-Flare Blitz/Earthquake
-Dragon Claw/Earthquake
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/180 SDef/80 Spe
Item: Charizardite X
Ability: Blaze
or
-Flare Blitz
-Dragon Claw
-Earthquake/Substitute
-Roost
Nature: Adamant
EVs: 40 HP/252 Atk/216 Spe
Item: Charizardite X
Ability: Blaze
or
-Swords Dance
-Flare Blitz
-Outrage
-Tailwind
Nature: Adamant
EVs: 40 HP/252 Atk/216 Spe
Item: Charizardite X
Ability: Blaze
Heatran:
-Overheat/Fire Blast
-Flash Cannon
-Earth Power/Hidden Power (Ice)
-Stone Edge/Ancient Power
Nature: Timid
EVs: 28 HP/4 Def/252 SAtk/228 Spe
Item: Choice Scarf
or
-Lava Plume/Fire Blast
-Taunt
-Toxic
-Stealth Rock
Nature: Timid
EVs: 248 HP/8 SAtk/252 Spe (Lava Plume) or 252 SAtk/4 SDef/252 Spe (Fire Blast)
Item: Leftovers/Air Balloon
or
-Lava Plume
-Toxic
-Taunt/Roar
-Stealth Rock/Protect/Earth Power
Nature: Calm
EVs: 248 HP/192 SDef/68 Spe
Item: Leftovers
or
-Magma Storm
-Earth Power
-Taunt
-Toxic
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Leftovers/Air Balloon
Mega Camerupt:
-Fire Blast
-Earth Power
-Ancient Power
-Will-o-Wisp/Stealth Rock/Toxic
Nature: Modest
EVs: 168 HP/252 SAtk/88 Spe
Item: Cameruptite
Ability: Solid Rock
Samurott is outclassed by other Water Pokemon, the most notable ones being Azumarill, Keldeo and Starmie:
Azumarill:
-Waterfall
-Play Rough
-Aqua Jet
-Knock Off/Superpower
Nature: Adamant
EVs: 164 HP/252 Atk/92 Spe (Choice Band) or 240 HP/252 Atk/16 SDef (Assault Vest)
Item: Choice Band/Assault Vest
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Knock Off
Nature: Adamant
EVs: 92 HP/252 Atk/164 Spe
Item: Sitrus Berry
Ability: Huge Power
Keldeo:
-Hydro Pump
-Secret Sword
-Icy Wind
-Scald
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Scarf/Choice Specs/Life Orb
or
-Substitute
-Calm Mind
-Scald
-Secret Sword
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Leftovers
Starmie:
-Scald
-Rapid Spin/Psyshock
-Reflect Type
-Recover
Nature: Timid
EVs: 248 HP/16 Def/244 Spe
Item: Leftovers
Ability: Natural Cure
or
-Hydro Pump
-Psyshock/Thunderbolt
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure/Analytic
Steelix is outclassed by other defensive Steel Pokemon like Ferrothorn. Its Defense is huge sure, but it has more weaknesses to take advantage of. Ferrothorn has a good set of resistances to use:
-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