First time posting in RMT, but not the first team I've built. Well...here goes
WARNING: This team is stally.
Scizor-Mega@Scizorite
Light Metal (Technician)
Impish Nature
248Hp 84Def 176SDef
Bullet Punch
Knock Off
Swords Dance
Roost
Not much preamble, as this is the 'mon I wanted the team built around anyway. The spread is the standard spread, but I moved the Attack EVs to Defense to make LO Drill have a 23% 2HKO chance w/o rocks (beforehand it would 2HKO you majority of the time), and like the standard spread nothing weaker than non-LO 252+ Landorus-Therian 2HKOs you on the physical end. Special Defense EVs make Modest max Special Attack M-Gardevoir not 2HKO you with Focus Blast or OHKO you with HP Fire (stock, mind you). It finds a lot of free turns to either boost up or spam Knock Off to remove items.
As for its ability in the meta, it counters a suprising number of threats. Weavile never touches you, I already mentioned M-Voir, M-Beedrill can't touch you, Fire-less Faries are walled, and defensive Lando-T and non-Taunt Gliscor are setup bait. Furthermore, it handles problems for the rest of the team, but I'll explain that later.
Heatran@Leftovers
Flash Fire
Calm Nature
248Hp 220Spd 32Spe
Lava Plume
Earth Power
Stealth Rock
Roar
Not a complicated set, but works well with Scizor. Earth Power + Flash Fire removes the (grounded) pesky Fire Types that give Scizor fits, notably always 2HKOing other heatran (fully specially defensive needs to be under ~70% to be OHKOed). Stealth Rock deals with the non-grounded ones (which I have switch-ins for anyway) as well as being helpful in general. Roar lets you beat Wish Passers (Sylv and Clef are the most common ones I send this in on) and other odd things like QD Volcarona/SubDisable Gengar. Lava Plume spamming also helps soften up things for Scizor to sweep later on.
As for its pains, that mainly comes from water-types. Earth Power is nice for denting them, but its not perfect. Scizor also has problems with Scald-Spammers, and therein lies the role of:
Tentacruel@Black Sludge
Liquid Ooze
Calm Nature
252Hp 224SDef 32Spe
Scald
Acid Spray
Toxic
Rapid Spin
An odd pick for OU, but fills a niche for my team. I first saw a variant of this set in "Good Cores" up in Victory Road and liked it a lot, but modded it a bit. Mainly, I added Toxic. Toxic + Acid Spray beats any Calm Minding Water Type (especially MegaBro and Suicune). Scald is Scald, and Rapid Spin removes hazards. 32Spe is faster than any non-Mega TTar.
This served as primarily an anti-MegaBro addition, though I didn't encounter it once while I tested this. Acid Spray meant that CM + Fire Blast Clef was handled (meaning I didn't need Taunt on Heatran). For Scizor, it also counters Zard Y effectively (they never pack EQ nowadays, normally preferring Focus Blast for TTar and Heatran) and beats (most) Greninja (Extrasensory hurts but won't OHKO, while the ninja is always 2HKOed by scald). For me, the most problematic hazard setter is ferrothorn (who can cripple M-Zor with residual damage), and Tenta will beat it most of time with Scald Burns and Liquid Ooze Damage. Toxic was useful for spamming against Rain Teams (who this can stay around against for a while) and baiting in Electric Types like Zapdos/M-Mane/Rotom-W.
Quagsire@Leftovers
Unaware
Relaxed Nature
248Hp 252Def 8Spe
Scald
Earthquake
Toxic
Recover
While Tenta beats Zard Y, this fella handles Zard X. In addition, it handles BellyJet Azu (who has a habit of randomly setting up on me) and most SD attackers. You may be thinking 8 Speed EVs!?!?!? WTF!? but in fact, it lets you outpace uninvested M-Bro and Amoonguss (meaning you can EQ them if they are low enough or get off a last ditch Scald burn/Toxic).
Probably one of my favorite pokes beyond M-Zor, not a whole lot of physical attackers can 1v1 this with no grass move. Adamant LO Drill can potentially 2HKO you with EQ, but that's if you come in on it. Generally, I found it safe to spam Recover on switches/free turns unless I was confident I'd still be above 70%ish otherwise. It handles Zard X and (Grass-less) electric types along with dangerous setup attackers like M-Gallade and offensive non-Taunt SD Talonflame.
Sylveon@Leftovers
Pixilate
Bold Nature
252Hp 208Def 36SDef 12Spe
Hyper Voice
Wish
Protect
Heal Bell
The team's cleric. She handles Thundurus (Never 2HKOs stock, even with LO) and most Dragons (notably HP Fire+Surf Lati@s). 36SDef blocks the 2HKO from Lando-I's Earth Power (though I rarely saw them) 12Spe outpaces uninvested TTar, rest in Def with max HP to make the wishes as big as possible. Hyper Voice stings, even uninvested, most Dragons are OHKOed or 2HKOed easily. In fact, AV Conkeldurr is always 2HKOed by this set (proved useful when one randomly had Fire Punch for Scizor). One common threat to Scizor she 1v1s with ease is Chesnaught.
She likes Scizor coming in on stronger physical attacks or ones she is weak to while Heatran handles the special end. Her cleric support and added power helps dent stuff like Rotom-W (she beats non-Pain Split variants on her own, while Scizor can 1v1 defensive variants and she cures the burn). Bisharp is a nuisance if it comes in unscathed, though I caught many a Bisharp setting up and KO'd/dented them with a Hyper Voice. Fully Special Greninja, furthermore, never 2HKOs this set (Tenta handles the mixed variants relatively well).
Zapdos@Rocky Helmet
Pressure
Bold Nature
248Hp 240Def 20Spe
Discharge
Heat Wave
Roost
Toxic
First thing is no Defog. I didn't like the idea of Defog + Rapid Spin (with such an easily trappable Rocker) and I like the utility of this set anyway. Furthermore, Discharge + Rocky Helmet always KOs Mega Pinsir (Discharge 2HKOes if it doesnt hit you), so that is why I am taking Discharge's increased para chance over Thunderbolt's power. 248Hp reduces SR damage, 20 Spe outpaces Adamant Bisharp.
I wanted a flying type, as well as a M-Pinsir counter, and this came to mind. Furthermore, not many people expect Discharge or Toxic, so it has caught people off-guard. Notably, a Paralyzed Heatran is no longer a check to Scizor if it has enough SDs and Toxic cripples Rotom-W (who like to come in on this) and bulky Ground Types. Heat Wave can remove Ferrothorns and other Mega Scizors with 100% efficiency and does nice damage to Amoonguss and Chesnaught (if you opponent thinks your mono-attack electric).
Threats:
Manaphy--CM mono-attack variants lose to Tenta Acid Spraying, but Tail Glow can be a huge problem. Tenta isn't OHKOed by anything from Timid Tail Glow, but can only Toxic in return. If they lack Energy Ball/Rain Dance, however, Quag can beat them 1v1 if its poisoned. I didn't encounter a Tail Glow variant, however, but it is still a pain in my neck nonetheless.
Landorus-I--Nothing safely comes in on it 100% of the time if it has Sludge Wave for Sylveon, though Zapdos can take a hit and poison it and Scizor can remove its LO and 1v1 it.
Excadrill--Zapdos can handle it, but only if it isn't Rock Slide flinched, otherwise Adamant LO Drill 2HKOs the entire team at least. Scizor can 1v1 it by Knocking off its LO, but it still isn't easy.
Greninja--Depending on its coverage I can beat it, but finding out isn't exactly easy (Tenta handles most of them, though).
Leaf Blade M-Gallade--a rarity, to be sure, but can crack Quag and otherwise be a pain. Zap can beat it if it doesn't have Ice Punch and Sylveon beats it if it isn't boosting (i.e., Sub + 3 attacks or 4 attacks)
Gengar--Similar vein as the ninja, but less dangerous and more annoying. Notably, HP Fire will never OHKO M-Zor if it isn't LO and it cannot OHKO Heatran unless its has Choice Specs. SubDisable loses to Scizor and Heatran.
There you have it. If there is anything I missed, let me know.
WARNING: This team is stally.
Scizor-Mega@Scizorite
Light Metal (Technician)
Impish Nature
248Hp 84Def 176SDef
Bullet Punch
Knock Off
Swords Dance
Roost
Not much preamble, as this is the 'mon I wanted the team built around anyway. The spread is the standard spread, but I moved the Attack EVs to Defense to make LO Drill have a 23% 2HKO chance w/o rocks (beforehand it would 2HKO you majority of the time), and like the standard spread nothing weaker than non-LO 252+ Landorus-Therian 2HKOs you on the physical end. Special Defense EVs make Modest max Special Attack M-Gardevoir not 2HKO you with Focus Blast or OHKO you with HP Fire (stock, mind you). It finds a lot of free turns to either boost up or spam Knock Off to remove items.
As for its ability in the meta, it counters a suprising number of threats. Weavile never touches you, I already mentioned M-Voir, M-Beedrill can't touch you, Fire-less Faries are walled, and defensive Lando-T and non-Taunt Gliscor are setup bait. Furthermore, it handles problems for the rest of the team, but I'll explain that later.
Heatran@Leftovers
Flash Fire
Calm Nature
248Hp 220Spd 32Spe
Lava Plume
Earth Power
Stealth Rock
Roar
Not a complicated set, but works well with Scizor. Earth Power + Flash Fire removes the (grounded) pesky Fire Types that give Scizor fits, notably always 2HKOing other heatran (fully specially defensive needs to be under ~70% to be OHKOed). Stealth Rock deals with the non-grounded ones (which I have switch-ins for anyway) as well as being helpful in general. Roar lets you beat Wish Passers (Sylv and Clef are the most common ones I send this in on) and other odd things like QD Volcarona/SubDisable Gengar. Lava Plume spamming also helps soften up things for Scizor to sweep later on.
As for its pains, that mainly comes from water-types. Earth Power is nice for denting them, but its not perfect. Scizor also has problems with Scald-Spammers, and therein lies the role of:
Tentacruel@Black Sludge
Liquid Ooze
Calm Nature
252Hp 224SDef 32Spe
Scald
Acid Spray
Toxic
Rapid Spin
An odd pick for OU, but fills a niche for my team. I first saw a variant of this set in "Good Cores" up in Victory Road and liked it a lot, but modded it a bit. Mainly, I added Toxic. Toxic + Acid Spray beats any Calm Minding Water Type (especially MegaBro and Suicune). Scald is Scald, and Rapid Spin removes hazards. 32Spe is faster than any non-Mega TTar.
This served as primarily an anti-MegaBro addition, though I didn't encounter it once while I tested this. Acid Spray meant that CM + Fire Blast Clef was handled (meaning I didn't need Taunt on Heatran). For Scizor, it also counters Zard Y effectively (they never pack EQ nowadays, normally preferring Focus Blast for TTar and Heatran) and beats (most) Greninja (Extrasensory hurts but won't OHKO, while the ninja is always 2HKOed by scald). For me, the most problematic hazard setter is ferrothorn (who can cripple M-Zor with residual damage), and Tenta will beat it most of time with Scald Burns and Liquid Ooze Damage. Toxic was useful for spamming against Rain Teams (who this can stay around against for a while) and baiting in Electric Types like Zapdos/M-Mane/Rotom-W.
Quagsire@Leftovers
Unaware
Relaxed Nature
248Hp 252Def 8Spe
Scald
Earthquake
Toxic
Recover
While Tenta beats Zard Y, this fella handles Zard X. In addition, it handles BellyJet Azu (who has a habit of randomly setting up on me) and most SD attackers. You may be thinking 8 Speed EVs!?!?!? WTF!? but in fact, it lets you outpace uninvested M-Bro and Amoonguss (meaning you can EQ them if they are low enough or get off a last ditch Scald burn/Toxic).
Probably one of my favorite pokes beyond M-Zor, not a whole lot of physical attackers can 1v1 this with no grass move. Adamant LO Drill can potentially 2HKO you with EQ, but that's if you come in on it. Generally, I found it safe to spam Recover on switches/free turns unless I was confident I'd still be above 70%ish otherwise. It handles Zard X and (Grass-less) electric types along with dangerous setup attackers like M-Gallade and offensive non-Taunt SD Talonflame.
Sylveon@Leftovers
Pixilate
Bold Nature
252Hp 208Def 36SDef 12Spe
Hyper Voice
Wish
Protect
Heal Bell
The team's cleric. She handles Thundurus (Never 2HKOs stock, even with LO) and most Dragons (notably HP Fire+Surf Lati@s). 36SDef blocks the 2HKO from Lando-I's Earth Power (though I rarely saw them) 12Spe outpaces uninvested TTar, rest in Def with max HP to make the wishes as big as possible. Hyper Voice stings, even uninvested, most Dragons are OHKOed or 2HKOed easily. In fact, AV Conkeldurr is always 2HKOed by this set (proved useful when one randomly had Fire Punch for Scizor). One common threat to Scizor she 1v1s with ease is Chesnaught.
She likes Scizor coming in on stronger physical attacks or ones she is weak to while Heatran handles the special end. Her cleric support and added power helps dent stuff like Rotom-W (she beats non-Pain Split variants on her own, while Scizor can 1v1 defensive variants and she cures the burn). Bisharp is a nuisance if it comes in unscathed, though I caught many a Bisharp setting up and KO'd/dented them with a Hyper Voice. Fully Special Greninja, furthermore, never 2HKOs this set (Tenta handles the mixed variants relatively well).
Zapdos@Rocky Helmet
Pressure
Bold Nature
248Hp 240Def 20Spe
Discharge
Heat Wave
Roost
Toxic
First thing is no Defog. I didn't like the idea of Defog + Rapid Spin (with such an easily trappable Rocker) and I like the utility of this set anyway. Furthermore, Discharge + Rocky Helmet always KOs Mega Pinsir (Discharge 2HKOes if it doesnt hit you), so that is why I am taking Discharge's increased para chance over Thunderbolt's power. 248Hp reduces SR damage, 20 Spe outpaces Adamant Bisharp.
I wanted a flying type, as well as a M-Pinsir counter, and this came to mind. Furthermore, not many people expect Discharge or Toxic, so it has caught people off-guard. Notably, a Paralyzed Heatran is no longer a check to Scizor if it has enough SDs and Toxic cripples Rotom-W (who like to come in on this) and bulky Ground Types. Heat Wave can remove Ferrothorns and other Mega Scizors with 100% efficiency and does nice damage to Amoonguss and Chesnaught (if you opponent thinks your mono-attack electric).
Threats:
Manaphy--CM mono-attack variants lose to Tenta Acid Spraying, but Tail Glow can be a huge problem. Tenta isn't OHKOed by anything from Timid Tail Glow, but can only Toxic in return. If they lack Energy Ball/Rain Dance, however, Quag can beat them 1v1 if its poisoned. I didn't encounter a Tail Glow variant, however, but it is still a pain in my neck nonetheless.
Landorus-I--Nothing safely comes in on it 100% of the time if it has Sludge Wave for Sylveon, though Zapdos can take a hit and poison it and Scizor can remove its LO and 1v1 it.
Excadrill--Zapdos can handle it, but only if it isn't Rock Slide flinched, otherwise Adamant LO Drill 2HKOs the entire team at least. Scizor can 1v1 it by Knocking off its LO, but it still isn't easy.
Greninja--Depending on its coverage I can beat it, but finding out isn't exactly easy (Tenta handles most of them, though).
Leaf Blade M-Gallade--a rarity, to be sure, but can crack Quag and otherwise be a pain. Zap can beat it if it doesn't have Ice Punch and Sylveon beats it if it isn't boosting (i.e., Sub + 3 attacks or 4 attacks)
Gengar--Similar vein as the ninja, but less dangerous and more annoying. Notably, HP Fire will never OHKO M-Zor if it isn't LO and it cannot OHKO Heatran unless its has Choice Specs. SubDisable loses to Scizor and Heatran.
There you have it. If there is anything I missed, let me know.