Here's a crazy idea for a Legendary:

Name: Manoxolf
Type: Dark/Fire
Ability: Reverse Field
All effects onstage are reverted.
(Which means burn now heals and doubles attack, healing such as recover and leftovers damages, stealth rock heals, rain weakens water moves but power up fire moves, stat buff becomes drops and vice versa, etc.)
Egg Group: Undetermined

Stats:
HP: 90
Atk: 110
Def: 50
SpA: 160
SpD: 50
Speed: 150

Base Stat Total: 610

Stat Ratings:
HP: 321
Atk: 256
Def: 136
SpA: 356
SpD: 136
Speed: 0.992079

PT: 85.634986
ST: 86.481152
PS: 216.952784
SS: 340.529204
ODB: 40.362311
PSB: -18.189756

Overall Rating: 416.017436
Moveset:
Level Up:
Start - Fire Fang
Start - Pursuit
9 - Amnesia
14 - Flame Charge
20 - Ancient Power
22 - Will-O-Wisp
31 - Trick
36 - Slash
44 - Magic Coat
49 - Crunch
51 - Nasty Plot
55 - Dark Pulse
63 - Fire Blast
68 - Cosmic Power
71 - Overheat
74 - Zen Headbutt
86 - Hyper Beam
99 - BurningRush*
100 - Spell Blast**

TM Moves:
TM02 - Dragon Claw
TM05 - Roar
TM08 - Bulk Up
TM11 - Sunny Day
TM12 - Taunt
TM15 - Hyper Beam
TM21 - Frustration
TM27 - Return
TM28 - Dig
TM30 - Shadow Ball
TM35 - Flamethrower
TM38 - Fire Blast
TM43 - Flame Charge
TM46 - Thief
TM54 - False Swipe
TM56 - Fling
TM61 - Will-O-Wisp
TM63 - Embargo
TM65 - Shadow Claw
TM66 - Payback
TM75 - Swords Dance
TM77 - Psych Up
TM84 - Poison Jab
TM90 - Substitude
TM93 - Wild Charge
TM95 - Snarl
HM01 - Cut
HM04 - Strength

Tutoring:
Uproar
Iron Head
Foul Play
Dark Pulse
Dragon Pulse
Hyper Voice
Zen Headbutt
Iron Tail
Aqua Tail
Heat Wave
Snatch

*Signature Move - BurningRush:
Type: Fire
Category: Physical
PP: 15 (Max 24)
Power: 85
Accuracy: 90%
Makes Contact
Affected by King's Rock
Not affected by Magic Coat, Snatch or Protect

Affects any opponent in Triple Battles

Description: Wrapping itself in flame, the user rams the target. This move ignores any type of protection (e.g.Protect, Detect, Substitude etc.) and has an increased priority.

**Signature Move - Spell Blast:
Type: Dark
Category: Special
PP: 10 (Max 16)
Power: 60
Accuracy: 100%
Does not make Contact
Affected by Protect and King's Rock
Not affected by Magic Coat or Snatch

Affects any opponent in Triple Battles

Description: The user concentrated the power on its body and launches at the target.(Further description: If the user is inflicted a status, the move deals an additional Power 60 hit with varied type:
Fire: Burn, Fire Spin, Magma Storm
Electric: Paralysis
Poison: Poison, Toxic
Ice: Freeze
Psychic: Sleep, Infatuation, Encore
Dark: Taunt, Torment
Ghost: Curse, Bind
Grass: Leech Seed, Wrap
Water: Clamp, Whirlpool
Ground: Sand Tomb
All statuses will be cured before launching the move.)

Manoxolf is a mon that is intentionally designed to wreck the whole Uber metagame. With its ability, stage hazards become useless as it instead heals, statuses becomes a blessing to both sides, and weather teams will be utterly wrecked. In +2 Sp.Attack, a Spell Blast with one status can 1HKO over half of the Uber tier, and those that aren't are also 2HKOed with the exception of Uber Support Arceus Dark/Chansey.If there are over 3 statuses, almost everything are 1HKOed. BurningRush can break through substitudes, and it being a priority move make it a threat to many substitude users.

Yet another Legendary:

Name: Drachence
Type: Steel/Electric
Ability: Hover Tank
Immune to Ground-Type moves and Gravity, Flying-Type moves gets STAB, Doubles Speed
Egg Group: Undetermined

Stats:
HP: 100
Atk: 80
Def: 160
SpA: 70
SpD: 150
Speed: 50 (100 with ability)

Base Stat Total: 610

Stat Ratings:
HP: 341
Atk: 196
Def: 356
SpA: 176
SpD: 336
Speed: 0.285149 (0.871287 with ability)

PT: 271.830239
ST: 249.559384
PS: 85.239005 (136.188067 with ability)
SS: 89.754803 (138.309970 with ability)
ODB: -29.487621 (-21.710982 with ability)
PSB: 2.595671 (2.945643 with ability)

Overall Rating: 394.248642 (459.463362 with ability)

Moveset:
Level Up:
Start - ThunderShock
Start - Scratch
6 - Wing Attack
13 - Hypnosis
19 - Air Cutter
27 - Thunder Wave
35 - Poison Gas
41 - Pound
46 - Discharge
52 - Steel Wing
58 - Iron Defense
65 - Volt Switch
69 - Iron Head
72 - Tailwind
73 - Bounce
77 - Overheat
83 - Venoshock
89 - Hyper Beam
99 - Hover Smash*
100 - Data Drain**

TM Moves:
TM01 - Hone Claws
TM02 - Dragon Claw
TM03 - Psyshock
TM04 - Calm Mind
TM09 - Venoshock
TM13 - Ice Beam
TM15 - Hyper Beam
TM16 - Light Screen
TM21 - Frustration
TM22 - Solar Beam
TM24 - Thunderbolt
TM27 - Return
TM29 - Psychic
TM33 - Reflect
TM35 - Flamethrower
TM52 - Focus Blast
TM53 - Energy Ball
TM54 - False Swipe
TM61 - Will-O-Wisp
TM65 - Shadow Claw
TM70 - Flash
TM72 - Volt Switch
TM73 - Thunder Wave
TM74 - Gyro Ball
TM82 - Dragon Tail
TM91 - Flash Cannon
TM93 - Wild Charge
TM90 - Substitude
TM95 - Snarl
HM01 - Cut
HM02 - Fly
HM04 - Strength

Tutoring:
Bounce
Signal Beam
Iron Head
Gunk Shot
Iron Defense
Dark Pulse
Dragon Pulse
Iron Tail
Aqua Tail
Sky Attack
Giga Drain
Tailwind

*Signature Move - Hover Smash:
Type: Steel
Category: Physical
PP: 15 (Max 24)
Power: 80
Accuracy: 100%
Makes Contact
Affected by King's Rock and Protect
Not affected by Magic Coat or Snatch

Affects adjacent opponent in Triple Battles

Description: The user smashes into the target. The move doubles in power when the user is levitating (e.g. Levitate, Hover Tank, Flying-Types)

**Signature Move - Data Drain:
Type: Electric
Category: Special
PP: 5 (Max 8)
Power: 100
Accuracy: 100%
Does not make Contact
Affected by Protect, King's Rock and Magic Coat
Not affected by Snatch

Affects any opponent in Triple Battles

Description: The user drains the power of the target through wires wrapped onto the target's body. The target's highest stat (counting modifiers) will drop while the user's corresponding stat rises.

Drachence is kind of a mixed sweeper/tank, with its signature moves, Hover Smash can 1HKO or 2HKO about 2/3 of the Uber tier with +2, and Data Drain on its own with +3 can also 2HKO half of the tier. Data Drain can also cripple the opponent by taking away their buffs and adding that on Drachence. With a +4 in attack alone, the whole tier can be at most 2HKOed by a combination of Hover Tank, Aqua Tail and Flamethrower, with Data Drain used for stat boost. On its defense side, only less than 1/4 of the tier can 1HKO it, WITHOUT STAT MODIFIERS. Once Drachence get +2 in both defense, nothing can hope to 1HKO it, and those who can 2HKO are very rare.

Another one Legendary:

Name: Photorn
Type: Psychic/Electric
Ability: Curved Light
Electric-Type Special Attack that misses has a 5% chance of hitting back in the start of the next round. Not affected by Protect.
Egg Group: Undetermined

Stats:
HP: 40
Atk: 120
Def: 40
SpA: 160
SpD: 60
Speed: 160

Base Stat Total: 580

Stat Ratings:
HP: 221
Atk: 276
Def: 116
SpA: 356
SpD: 156
Speed: 0.996040

PT: 42.475243
ST: 65.372040
PS: 242.263125
SS: 342.286774

ODB: 44.024659
PSB: -17.970153

Overall Rating: 391.636068
(Not bad, it's a legendary after all. Not surprised by its bad tanking ratings, but the Special Sweeping... that's high.)

Moveset:
Level Up:
Start - Thunder Wave
Start - Tackle
6 - Confusion
13 - Charge Beam
19 - Agility
22 - Volt Switch
30 - AncientPower
37 - Extrasensory
42 - Nasty Plot
48 - Psychic
53 - Thunderbolt
64 - Electro Ball
75 - ElectroBlast*
76 - PositroBlast**

TM Moves:
TM03 - Psyshock
TM04 - Calm Mind
TM10 - Hidden Power
TM15 - Hyper Beam
TM16 - Light Screen
TM17 - Protect
TM21 - Frustration
TM24 - Thunderbolt
TM25 - Thunder
TM27 - Return
TM29 - Psychic
TM30 - Shadow Ball
TM32 - Double Team
TM33 - Reflect
TM40 - Aerial Ace
TM48 - Round
TM52 - Focus Blast
TM53 - Energy Ball
TM54 - False Swipe
TM57 - Charge Beam
TM66 - Payback
TM70 - Flash
TM71 - Stone Edge
TM72 - Volt Switch
TM73 - Thunder Wave
TM75 - Swords Dance
TM81 - X-Scissor
TM89 - U-turn
TM90 - Substitude
TM93 - Wild Charge
HM01 - Cut
HM02 - Fly

Tutoring:
Signal Beam
Dual Chop
Fire Punch
ThunderPunch
Ice Punch
Last Resort
Iron Defense
Magic Coat
Zen Headbutt
Bind
Role Play
Drain Punch
Trick
Sleep Talk
Skill Swap

*New Move - ElectroBlast:
Type: Electric
Category: Special
PP: 10 (Max 16)
Power: 95
Accuracy: 85%
Does not make Contact
Affected by King's Rock and Protect
Not affected by Magic Coat or Snatch

Affects adjacent opponent in Triple Battles

Description: The user releases a blast of electron at the target. This move reduces the user's Special Defense.

**New Move - PositroBlast:
Type: Electric
Category: Special
PP: 10 (Max 16)
Power: 95
Accuracy: 85%
Does not make Contact
Affected by King's Rock and Protect
Not affected by Magic Coat or Snatch

Affects adjacent opponent in Triple Battles

Description: The user releases a blast of positron at the target. This move reduces the user's Defense.

When both ElectroBlast and PositroBlast are used, everyone on field receives damage equal to 1/8 of their maximum HP, taking Type Resistance and Weakness into account.

Photorn is your typical sweeper, but his ability ramps his power even more. Without the ability, Photorn can already rip through almost all of Uber tier to OU tier at SpA +2. At +3, Chansey is usually 2HKOed. However, Photorn is frail, and subspectible to two priority moves, which means it has a high chance of dying if the opponent survives its attacks.

Another Legendary...yet:

Name: Gravitorn
Type: Psychic/Ground
Ability: Gravity Field
All Pokemon over 30 kg are trapped. Ground-Type immunities are disabled, except Hover Tank.
Egg Group: Undetermined

Stats:
HP: 70
Atk: 80
Def: 190
SpA: 40
SpD: 170
Speed: 30

Base Stat Total: 580

Stat Ratings:
HP: 281
Atk: 196
Def: 416
SpA: 116
SpD: 376
Speed: 0.061386

PT: 261.052279
ST: 229.048135
PS: 70.943546
SS: 52.366750

ODB: -30.774242
PSB: 7.394598

Rating: 339.868613
(Hmmm... Isn't as good as I imagine, apparently it's because of its low sweeping ability.)

Moveset:
Level Up:
Start - Bulk Up
Start - Smack Down
10 - Spike
15 - Mud Bomb
23 - Cosmic Power
28 - Harden
34 - Spike Cannon*
39 - Psycho Cut
44 - Quash
50 - Head Smash
57 - Earthquake
66 - Cross Chop
71 - Mirror Coat
78 - Trick Room

TM Moves:
TM03 - Psyshock
TM04 - Calm Mind
TM06 - Toxic
TM08 - Bulk Up
TM12 - Taunt
TM16 - Light Screen
TM17 - Protect
TM21 - Frustration
TM23 - Smack Down
TM26 - Earthquake
TM27 - Return
TM28 - Dig
TM29 - Psychic
TM31 - Brick Break
TM33 - Reflect
TM37 - Sandstorm
TM39 - Rock Tomb
TM40 - Aerial Ace
TM52 - Focus Blast
TM60 - Quash
TM61 - Will-O-Wisp
TM67 - Retaliate
TM71 - Stone Edge
TM73 - Thunder Wave
TM74 - Gyro Ball
TM75 - Swords Dance
TM78 - Bulldoze
TM80 - Rock Slide
TM83 - Work Up
TM90 - Substitude
TM92 - Trick Room
TM94 - Rock Smash
HM01 - Strength
HM02 - Fly

Tutoring:
Iron Head
Dual Chop
Fire Punch
ThunderPunch
Ice Punch
Iron Defense
Magic Coat
Earth Power
Superpower
Zen Headbutt
Gravity
Drain Punch
Pain Split
Magic Room
Wonder Room
Stealth Rock
Endeavor

*New Move - Spike Cannon
Type: Ground
Category: Physical
PP: 20 (Max 32)
Power: 80
Accuracy: 90%
Does not make Contact
Affected by King's Rock, Protect and Magic Coat
Not affected by Snatch

Affects adjacent opponent in Triple Battles

Description: The user throws a bunch of spikes at the target. This move lays spikes on the opponent's field, with a 5% chance of laying down 2 layers.

Gravitorn is sort of a wall, but it can attack with high power too. Even though its typing leave it with quite a few disadvantageous weaknesses such as Water and Dark, Gravitorn learns Stealth Rock, Spike and Spike Cannon which can deal damage while laying down stage hazards. It also learn a few moves that buff both defense, and at +2 SpD only around 1/5 of both OU and Uber tier can possibly 2HKO it. It also has an alright 80 attack, able to 2HKO half of the OU-Uber Tier in +2 Attack.

I've always thought, especially upon entering the competitive field of Pokemon, that it would be a good idea to have a Pokemon that punishes opponents for using non-attacking moves, especially stat-boosting moves.
In order for it to be effective, you'd have to make some sort of ability like Magic Bounce, but also copies the opponent's stat changes, or just have a really fast one with Taunt!

The last of the Particle Trio, with the previous Photorn and Gravitorn, Antitorn is here!

Name: Antitorn
Type: Psychic/Dark
Ability: Annihilate
When hit by Psychic/Dark-Type moves, every mon onfield receive damage equal to 1/2 max HP.
Egg Group: Undetermined

Stats:
HP: 100
Atk: 60
Def: 90
SpA: 70
SpD: 100
Speed: 160

Base Stat Total: 580

Stat Ratings:
HP: 341
Atk: 156
Def: 216
SpA: 176
SpD: 236
Speed: 0.996040

PT: 157.488055
ST: 171.147544
PS: 110.014631
SS: 132.724843

ODB: -6.480070
PSB: -5.317009

Overall Rating = 312.318605
(Apparently speedy mons with low attack stats get a lower rating, but at least it is viable.)

Moveset:
Level Up:
Start - Taunt
Start - Confusion
8 - Pursuit
16 - Hypnosis
21 - Frost Breath
28 - Snarl
32 - Psybeam
39 - Tri Attack
44 - Nasty Plot
53 - Psychic
57 - Dark Pulse
63 - Ice Beam
70 - Uproar
75 - Void Crush*

TM Moves:
TM03 - Psyshock
TM04 - Calm Mind
TM06 - Toxic
TM09 - Venoshock
TM10 - Hidden Power
TM13 - Ice Beam
TM15 - Hyper Beam
TM17 - Protect
TM21 - Frustration
TM27 - Return
TM29 - Psychic
TM30 - Shadow Ball
TM32 - Double Team
TM34 - Sludge Wave
TM40 - Aerial Ace
TM41 - Torment
TM46 - Thief
TM52 - Focus Blast
TM56 - Fling
TM60 - Quash
TM61 - Will-O-Wisp
TM65 - Shadow Claw
TM66 - Payback
TM67 - Retaliate
TM79 - Frost Breath
TM85 - Dream Eater
TM87 - Swagger
TM89 - U-turn
TM90 - Substitude
TM95 - Snarl
HM01 - Cut
HM04 - Strength

Tutoring:
Signal Beam
Gunk Shot
Magic Coat
Block
Icy Wind
Zen Headbutt
Foul Play
Dark Pulse
Bind
Snore
Knock Off
Pain Split
Spite
Trick
Endeavor
Sleep Talk
Snatch

*New Move - Void Crush:
Type: Dark
Category: Special
PP: 5 (Max 16)
Power: 110
Accuracy: 75%
Does not make Contact
Affected by King's Rock
Not affected by Magic Coat, Protect or Snatch

Affects any opponent in Triple Battles

Description: The user traps the target in a void, then destroys it. All stats of the target harshly drops and the target lose its held item, but the user must recharge after the move.

Antitorn is a balanced mon: It can give off statuses and stall, or act as a mixed tank-sweeper. Its high 160 speed and good 100 HP helps this too. With +2 in Sp.Attack, Antitorn can surprisingly 2HKO many of the Uber tier with a combination of Void Crush and Psychic. Add in the other coverage moves, this spirit of antimatter is quite hard to face.

Deathgeam HP: 80 | Shadow Pulse: 90 Power, 85 Accuracy 10 PP Special
Ghost/Psychic Atk: 30 | 20% chance of paralyzing
Ability: Def: 40 | Shadow Cloud: --- Power --- Accuracy 5 PP Summons a shadowy cloud for 5 turns.
Undead Shield SpA: 100 | All non Ghost or Dark pokemon take 1/16 Max. HP and speed is halved.
Halves damage received SpD: 210 |
from physical moves above Spe: 70 |
70 power. |
–––––––––––––––––––––––---------------
Moves|
--------
Via Level:
Start: Confusion
Start: Confuse Ray
7: Agility
9: Shadow Ball
14: Cosmic Power
17: Hex
19: Shadow Punch
20: Calm Mind
24: Shadow Claw
28: Hone Claws
34: Amnesia
38: Hypnosis
46: Shadow Cloud (New move)

TMs:
TM06 Toxic
TM10 Hidden power
TM11 Sunny Day
TM12 Taunt
TM16 Light Screen
TM17 Protect
TM29 Psychic
TM41 Torment
TM42 Facade
TM44 Rest
TM46 Theif
TM48 Round
TM66 Payback
TM95 Snarl
TM96 Shadow Pulse (New move, See side notes)

This pokemon is very special-based, with good status moves and terrifyingly bad HP and physical stats.

How about a Water-Type Major Status Problem called Wet? This decrease the Sp.Attack by 2 on victim and such victim's ability is also disactivated. Water-Type Pokémon and Pokémon that are immune to Water-Type via ability are immune to this.

Good against Kyurem-W and other special sweepers.

Hmm... I may just start making Pokemon again sometime soon...