Defensive Core

Alomomola @ Leftovers
Trait: Regenerator
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- Waterfall
- Toxic
- Protect
- Wish

Regice @ Leftovers
Trait: Clear Body
EVs: 240 HP / 252 SAtk / 16 Spe
Modest Nature
- Ice Beam
- Thunderbolt
- Rest
- Sleep Talk
This is a simple defensive combination consisting of a physical wall and a special wall. Most special attackers like Exeggutor or Rotom-S that eat Alomomola up can be handled nicely by Regice while Alomomola can take care of powerful physical attackers such as Emboar and Gurdurr. Regice has the added bonus of being able to absorb annoying status aimed at Alomomola and enjoys the huge wishes that the later passes to it.
Obviously, this core is not perfect. Stealth Rock is an Annoyer since it reduces Regice' ability to wall things such as Ludicolo and Gorebyss by having it take a fourth of its health everytime it comes in. Physical attackers that can beat Alomomola—such as Sawsbuck—or special attackers that can beat Regice—like Charizard—are also capable of muscling through this combo. Choice Band Sawk can 2HKO Alomomola, so a sturdy Fighting-type resist, which everyteam should have, is a good partner for this core. Other teammates to consider are Regirock, which beats most Fire-types, Torkoal, who has excellent type synergy with the core and can spin away hazards, or Misdreavus, which acts as an aforementioned Fighting-type switch-in and can use Heal Bell to wake up Regice and support Alomomola.