Heracross @ Heracronite
Ability: Guts / Moxie
EVs: 28 HP / 252 Atk / 228 Spd
Adamant Nature
- Pin Missile
- Close Combat
- Rock Blast
- Bullet Seed
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 4 SAtk / 252 SDef
Calm Nature
IVs: 0 Atk
- Lava Plume
- Stealth Rock
- Roar
- Toxic
This core is an offense / defense core, but I would say it's more of bulky offense. The idea here is that Mega Heracross can trample teams, but not if the opponent can Will-O-Wisp it, Toxic it, or send in Talonflame, Charizard, Aegislash, or Skarmory. Heatran just so happens to be able to stop those threats and wall quite a few of them. It sets up rocks and can phaze, which helps give Mega Heracross a little extra help against things it can't quite OHKO, and together, they cover each other's weaknesses, except water. However, water isn't a huge problem when Bullet Seed on Mega Hera can do damage such as:
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 0 Def Mega Blastoise: 340-410 (93.9 - 113.2%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 252 Def Rotom-W: 300-360 (98.6 - 118.4%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 252+ Def Milotic: 340-400 (86.2 - 101.5%) -- approx. 93.8% chance to OHKO after Stealth Rock
A lot of people would call me stupid for running Bullet Seed and not Earthquake. The reason for that is that Aegislash doesn't really warrant the move slot. I'd rather be able to kill Rotom-W and any other bulky water with Bullet Seed than to rely on Earthquake, a move people often expect and carry an Air Balloon for. Besides, this is a thing:
252+ Atk Mega Heracross Rock Blast (5 hits) vs. 252 HP / 0 Def Aegislash-Blade: 170-200 (52.4 - 61.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Another thing you might ask for are the reasons for Heracross' EVs. The EVs put Heracross ahead of Bisharp and Rotom-W in speed, as well as having maximum power.
The main threats to the core are physically defensive ground types. Hippowdon, Gliscor, etc. Hippowdon is easily 2HKO'd by Bullet Seed, but Gliscor is tougher to kill. On sets without EQ (Which exist, my Air Balloon Aegislash learned that the hard way), Heatran's Roar can go through their sub, making them less of a pain at the moment. Another problem can be bulky waters that predict the switch to Heracross and Will-O-Wisp. To be fair, it would be strange to keep Heatran in on a water type.
Bulky grass types are great friends to the core, specifically Celebi. Physically defensive Celebi with Thunder Wave can make it easier for Heracross to outspeed things and get free kills, and the bulkiness helps against physical attackers. Also, it's a great way to shrug off incoming status with Natural Care, and a good answer to those bulky water types and defensive ground types. Using the three of these Pokemon, you have a core that fits the standards of bulky offense.
Here are some replays:
http://replay.pokemonshowdown.com/ou-102300211
http://replay.pokemonshowdown.com/ou-100042612
http://replay.pokemonshowdown.com/ou-105678761