Just a few cores I've tried and have worked to some extent. Most of the EVs and moves are just sample sets, they can be extensively tinkered with.
OU:
Heatran/Ferrothorn/Gliscor(defensive)
(Heatran) (M) @ Leftovers
Trait: Flash Fire
EVs: 252 HP / 252 SDef / 4 Spd
Calm Nature (+SDef, -Atk)
- Earth Power
- Flamethrower
- Roar
- Stealth Rock
(Ferrothorn) (M) @ Leftovers
Trait: Iron Barbs
EVs: 252 HP / 8 Def / 248 SDef
Relaxed Nature (+Def, -Spd)
- Spikes
- Leech Seed
- Protect
- Gyro Ball
(Gliscor) (F) @ Toxic Orb
Trait: Poison Heal
EVs: 184 HP / 40 Atk / 136 Def / 148 Spd
Impish Nature (+Def, -SAtk)
- Protect
- Fling
- Earthquake
- Acrobatics
description: It's pretty obvious but it works hella well. Ferrothorn and Heatran set up hazards, phaze, and can threaten some Pokemon, such as those Fire weak, Grass weak, etc. Gliscor is a powerful phyiscal wall that neutralizes the fighting weakness and Ground weak/neutrality, being a physical wall is just great also in general considering the Specially defensive EVs of Ferrothorn and Heatran. The Gliscor set is a more defensive wall type but the also popular IceFang/EQ/SD/Taunt set can also work.
Jellicent/Forretress/Chansey(defensive)
(Jellicent) (M) @ Leftovers
Trait: Water Absorb
EVs: 248 HP / 216 Def / 44 Spd
Bold Nature (+Def, -Atk)
- Taunt
- Recover
- Will-O-Wisp
- Scald
note: Forry has 0 speed IV
(Forretress) (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 176 Atk / 80 SDef
Relaxed Nature (+Def, -Spd)
- Toxic Spikes
- Stealth Rock
- Rapid Spin
- Gyro Ball
(Chansey) (F) @ Eviolite
Trait: Natural Cure
EVs: 252 HP / 252 Def / 4 SDef
Bold Nature (+Def, -Atk)
- Aromatherapy
- Toxic
- Softboiled
- Seismic Toss
Pretty fucking annoying. Ferrothorn/Jellicent is a classic core that people should know and I'm not gonna post, but this expands on that with Forretress instead, who can set up more varied hazards. Chansey provides a really annoying wall for Special attackers that can rip down Jellicent with SE moves and Forretress just because it has poor SpDef. Jellicent is a great anti-stall mirror, with Taunt, and Chansey's Toxic or Forry's T Spikes easily whittle stuff down. Not that much else to say.
Will post more cores(added to this post) as I sort through my old teams.
Thundurus/Scizor(offensive)
(Thundurus) (M) @ Life Orb
Trait: Prankster
EVs: 252 SAtk / 4 SDef / 252 Spd
Timid Nature (+Spd, -Atk)
- Nasty Plot
- Thunderbolt
- Hidden Power [ice]
- Focus Blast
(Scizor) (M) @ Choice Band
Trait: Technician
EVs: 228 HP / 252 Atk / 28 Spd
Adamant Nature (+Atk, -SAtk)
- U-turn
- Bullet Punch
- Superpower
- Pursuit
Tenshi? Offensive? What has this world come to? The premise is pretty simple, Nasty Plot Thundurus is a ridiculous wrecking ball, its few counters include faster sweepers, Chansey(let's try our luck with +2 Focus Blasts!) and umm... Quagsire I guess? Scizor does an excellent job of assisting Thundurus, ripping through special walls, inflicting heavy damage to most fast and frail Pokemon that can scare out Thundurus, and tanking the ever so common Ice moves bound to be thrown at Thundurus, while Thundurus clears troublesome juggernauts such as Jellicent from Scizor's rampage.