Defensive core, Latias/Heatran
These two provide a whole ton of defensive synergy, in addition to utility such as status abosrbtion, hazard control and phazing. Between the two, they resist almost everything - Heatran may have lost its dark resistance (a key aspect of this core in previous generations), but it gained a fairy resistance which is huge in the current metagame. Heatran is weak to fighting, water and ground, which Latias is either immune to or resists, whereas Latias is weak to bug, ice, fairy - Heatran resists all these
x4 - along with dragon, which it resists too. Latias is hit super effective by dark and ghost types, which Heatran doesn't resist, but your team can easily remedy this by including an appropriate partner. Heatran also provides a neat x4 grass weakness, meaning Serperior can't touch it if it isn't running an appropriate Hidden Power.
This core has many other benefits beyond virtue of their typing. Heatran provides Stealth Rocks, which is always useful if not mandatory, and Latias provides Defog, which is extremely strong. Latias has the added benefit of being immune to Spikes/Toxic Spikes, meaning she can clear these for Heatran and her teammates without taking any damage. Heatran provides Roar, which is very useful given the popularity of boosting sweepers at the moment.
This core handles many top-tier threats, including, but not limited to; Clefable, Lopunny, Scizor, Lando-T (scarfed anyhow), Talonflame, Keldeo, opposing Heatran, Thundurus, Gardevoir, Venusaur, Excadrill, opposing Latias/Latios and M-Sceptile (but to name A-tier threats). It has trouble with certain Pokemon; non-scarfed Lando-T can be a pretty big deal, as U-Turns hurts Latias/Earthquake Heatran, but Latias can always smack is with a Draco Meteor if it switches into rocks. M-Heracross is a big threat to this core, OHKOing (but not outspeeding) both members. M-Gyarados can also be problematic, as are Pursuit variants of M-Metagross, but the number of threats this core covers far outweighs those it is threatened by.
Appropriate partners would include a strong physical wall, who can take on the likes of Heracross, Metagross and Gyarados. Skarmory jumps to mind, providing Spikes in addition to covering these threats, whilst Talonflame makes a decent offensive partner, taking on Heracross and Metagross.
Unsure on how to format the sets, but here they are;
Latias @ Life Orb
Ability: Levitate
EVs: 160 HP / 96 SpA / 252 Spe
Timid Nature
- Defog
- Draco Meteor
- Thunderbolt
- Roost
Heatran @ Leftovers
Ability: Flash Fire
EVs: 248 HP / 192 SpD / 68 Spe
Calm Nature
- Lava Plume
- Toxic
- Roar
- Stealth Rock