Torterra @ Leftovers
Ability: Overgrow  
EVs: 252 HP / 4 Atk / 252 Def  
Impish Nature  
- Wood Hammer  
- Earthquake  
- Stealth Rock  
- Synthesis
Torterra is a great physical wall and Stealth Rock setter in ZU, being able to threaten the majority of hazard removers and carrying reliable recovery, as well as just being one of the best ways to counter Lycanroc. However, Torterra serious faces issues in taking on Fire types and Ice type attacks.

Grumpig @ Mago Berry  
Ability: Thick Fat  
EVs: 252 HP / 80 Def / 176 Spe  
Timid Nature  
IVs: 0 Atk  
- Psychic  
- Focus Blast / Toxic
- Substitute  
- Recycle
Thick Fat grants Grumpig two free resistances, something that is incredibly useful. In this instance, both of those resistances are to types that Torterra is weak to. On top of that, the biggest Fire types for a player to prepare for are also Fighting type, which Grumpig also resists. Grumpig is also naturally bulky on the special side, meaning it covers Torterra's weakness to special attackers with Ice coverage handily while Torterra covers for Grumpig's low physical bulk.
---Teambuilding Weaknesses---
This core may be great against a very good number of high level threats in ZU, but also comes with serious weaknesses. A powerful U-Turn user, particularly Liepard, can abuse this core and an offensive Bug type is a nightmare to deal with, so partners that can address these issues are seriously important. Tangela with Knock Off is also a serious problem for this core, as Grumpig cannot recover Mago Berry if Tangela catches it with Knock Off and Torterra cannot do significant damage to Tangela, which can outlast Torterra through Giga Drain.