Generally speaking, Megas are the hardest hitters across all tiers in Gen 6. As they often lack the capacity to outright sweep due to poor speed's. So with that being said, here are some of the most prominent wallbreakers in OU/BL. (I wont go into to much details as I have quite many examples).
Charizard-Mega-X @ Charizardite X
Ability: Tough Claws
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Claw
- Dragon Dance/Sword Dance
- Flare Blitz
- Earthquake
First of is the first Charizard Mega. Its Ability along with its great boosting moves allow Charizard X to ravenge teams. It do require setup to properly wallbreak, but with the right support (particulary Sticky Web) this thing is lethal.
Charizard-Mega-Y @ Charizardite Y
Ability: Drought
EVs: 248 HP / 8 Atk / 252 SpA
Mild Nature
- Flamethrower/ Fire Blast
- Roost
- Solar Beam
- Earthquake
The second Charizard Mega requires little to no setup, since it really cant set up at all. Its 159 base SpAtk and Drought ability puts Reshiram to shame in turns of raw power. It do lack some truly usable STAB, and need to run EQ to get past Heatran, but it is nevertheless a nuke in power.
Pinsir-Mega @ Pinsirite
Ability: Aerilate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Return/Thrash/Double Edge
- Swords Dance
- Earthquake
- Knock Off/Stone Edge
Similar to the Charizard's, M-Pinsir's power lie in its Ability. With it it gains incredibly strong STAB from Return/Thrash/Double Edge, ready to kill of most things. Being unable to get past Zapdos and a Stealth Rock weakness hinder it somewhat, but it is a great wallbreaker with the proper support.
Terrakion @ Choice Band
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Close Combat
- Stone Edge
- Earthquake
- Iron Head
Terrakion hit hard last Gen and it's still packing a punch. Basically speaking it havn't changed much since last gen, its still walled by Gliscor and Landorus-I, and demolish everything else.
Gallade-Mega (M) @ Galladite
Ability: Inner Focus
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Swords Dance
- Drain Punch
- Ice Punch
- Knock Off
Straight out of ORAS M-Gallade stands at one of the most powerful new Megas. Acess to Drain Punch, Sword Dance and a great speed tier allow it to both sweep and wallbreak effectively. Paired that with good coverage just makes it a great Pokemon.
Manectric-Mega @ Manectite
Ability: Intimidate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Volt Switch
- Flamethrower
- Thunderbolt
- Hidden Power [Ice]
Despite a shallow movepool M-Manectric have just the coverage it need to be powerful. Acess to Intimidate and Fire coverage set it apart from the likes of Thundrus, and Volt Switch and good Speed set it apart from other Megas. Overall a great scout/wallbreaker.
Lopunny-Mega @ Lopunnite
Ability: Scrappy
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- High Jump Kick
- Ice Punch
- Substitute
- Return
M-Lopunny's access to an unresisted High Jump Kick and near perfect coverage with just its STABs makes this former NU Pokemon a true force of nature. It do lack things to properly do with its two extra moveslots, its still a powerful Pokemon with a solid 136 Atk and 135 Spe.
Talonflame @ Choice Band/Life Orb
Ability: Gale Wings
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Brave Bird
- Flare Blitz
- U-turn
- Roost/Sword Dance
Once again a Pokemon with a great ability makes an apperance. Gale Wing is just ridiculus, giving its already powerful Brave Bird amazing priority. Despite lackluster Atk and a SR weakness it have succesfully established itself as a great nieche sweeper/wallbreaker in Gen 6 OU.
Hawlucha @ Power Herb
Ability: Unburden
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Sky Attack
- High Jump Kick
- Acrobatics
- Stone Edge
From one bird to another, Hawlucha works quite diferently from Talonflame. It can really only run one set, making it quite easy to predict, but it still hits hard as nails. Sure, its the definition of a one-trick-pony, but its a good one-trick-pony.
Latios (M) @ Life Orb/Choice Specs
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Psyshock
- Hidden Power [Fire]
- Surf
- Draco Meteor
Similar to Tarrakion, Latios is still a solid wallbreaker. It was hurt more by the rise of Dark, Ghost and Fairy types, but it still hits really hard. With coverage and great power, its still amazing.
Medicham-Mega @ Medichamite/Choice Scarf
Ability: Pure Power
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Ice Punch
- High Jump Kick
- Psycho Cut
- Bullet Punch
One of the few Pokemon with a Mega that can function withouth it. With good coverage and equally good stats, it's a great Pokemon. Albeit not great due to a low Speed and being outclassed by the likes of M-Gallade, it is still a good wallbreaker.
Glalie-Mega @ Glalitite
Ability: Refrigerate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Explosion
- Ice Shard
- Earthquake
- Return
Rounding things of is the nuke of snow itself. Refrigerate makes a ordinarily powerful attack in Explosion a force to rival nature. It can take down pretty much anything with it, even though it have trouble with priority, and only being able to properly wallbreak one Pokemon. Still, it is the hardest hitter in Gen 6, and when used correctly it will finish anything of with ease, regardless of prior damage.
