Right, well I have a utility core I'd like to bring to the table; which, if you've seen me around, knows that this comes from my most prized team itself:
Barry (Bronzong) @ Leftovers
Ability: Levitate
EVs: 236 HP / 84 Atk / 20 SDef / 168 Def
Sassy Nature
IVs: 0 Spd
- Stealth Rock
- Gyro Ball
- Zen Headbutt
- Toxic
Amphabulous (Ampharos-Mega) (M) @ Ampharosite
Ability: Mold Breaker
EVs: 220 HP / 208 SDef / 80 SAtk
Calm Nature
IVs: 0 Atk
- Thunderbolt
- Dragon Pulse
- Focus Blast
- Volt Switch
Momo (Milotic) (F) @ Leftovers
Ability: Marvel Scale
EVs: 248 HP / 16 SAtk / 220 SDef / 24 Def
Calm Nature
IVs: 0 Atk
- Scald
- Ice Beam
- Mirror Coat
- Recover
Right, so, let me explain why this core could provide a great service to Team Defense. First off, all three members have outstanding bulk, with the only weak spot being Milotic's defense, but I'll get to that shortly. Secondly, they cover each other's weaknesses well, with the only one having imperfect synergy being Bronzong's dark and ghost weaknesses. And thirdly, none of them are severe offensive slouches, in more ways than one. Allow me to explain.
Milotic is the one I feel needs the most explaining. Right. So, Bronzong, while not an offensive titan, relies on some physical attacks to deal damage to pokemon it can't afford to stall out. Therefore, burns are an absolute no-no for the rainmaker. Milotic, however, is into some weird shit. Burns are a blessing to Milotic, as they whittle down a very small amount of HP when factoring in Leftovers, and with access to Recover, it barely scratches her. The reason Milotic loves burns so much is her fantastic ability in Marvel Scale, which is essentially a free defense curl that lasts throughout the entirety of the match. This turns Milotic into a massive mixed tank. So, switching into Scalds and Will-O-Wisps and Lava Plumes are all excellent roles for Milotic to fulfill. The moveset is fairly standard, bar Mirror Coat. Mirror Coat is there to mess up Char-Y. She has no problem switching into a sun boosted Fire Blast thanks to her titanic special bulk. After this, a Solarbeam is almost inevitable, which she easily tanks, and OHKOs every time with Mirror Coat. In my opinion, all Special Attack oriented pokemon should ALWAYS run a negative attack nature with 0 Atk IVs, as this results in the smallest possible damage output from Foul Play users.
Next, we have Bronzong. He is a reliable stealth rock setter, but there are many of those, so why him? Well lemme esplain a thing. A common lead on HO teams, which we have a good possibility of facing, is Deoxys-S. It's almost always safe to assume Deoxys-S will go for a mirror coat or a taunt, at which point you should outpredict and go for Gyro Ball, which 2HKOs Deoxys-S. In addition, this spread allows him to survive a Knock Off from both Conkeldurr and Azumarill at full health, guaranteeing you get SR up if no prior damage has been taken. As well, Zong can survive a Shadow Ball from Gengar at full health, and can OHKO with EITHER Zen Headbutt or Gyro Ball. Zen Headbutt is the preferred coverage option over earthquake, as it prevents you from being completely walled by the various fighting and poison types in the tier, such as Venusaur. Toxic is there to whittle down threats that can't do much damage to Bronzong in the instance that he can't do much damage back. Also, sidenote, Bronzong wins 1v1 with Mega Pinsir. Keep that in mind.
And finally, my personal favorite, Mega Ampharos. In addition to being flawless in every way, he's pretty bulky, and with this set can survive 2 Ice Beams from Greninja, or, as the preferred option would be, one ice beam and then proceed to Volt Switch to safety. Dragon Pulse can nail Garchomp, Gliscor, and Landorus-T on the switch, and Focus Blast slaughters Excadrill. Again, 0 Atk IVs is the preferred option here. Mega Amph is an extremely optimized Pivot Switch, and should be played as such. While it takes up a mega slot, if given the proper support, Ampharos can be a boon to any defensive team.
And there's my suggestion for this round. This core greatly appreciates a cleric like Blissey or Sylveon, as Milotic is the only one with instant recovery. Another good partner would be something that can take Charizard X, as unless he is hit on the switch, he plows through this core without much of a problem. And that's all I got for now.