Rotom-Frost @ Choice Scarf 
/ Icium Z
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Volt Switch
- Blizzard
- Trick / Pain Split
- Thunderbolt
Rotom-Frost is one of the most common and most effective offensive pivots in ZU, having excellent offensive coverage with its STAB moves. However, while Rotom-Frost may excel offensively, it isn't nearly as effective defensively, with some of its notable issues being that it is weak to Rock and Choice Scarf sets can be caught using Volt Switch with an Electric immunity and taken advantage of.

Torterra @ Leftovers 
/ Occa Berry
Ability: Overgrow
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- Wood Hammer
- Earthquake
- Stealth Rock
- Synthesis
Torterra acts as a great defensive backup for Rotom-Frost to pivot into for safety, countering most Rock types that would otherwise try to threaten Rotom-Frost and countering many Ground types that could take advantage of a choice locked Rotom-Frost. Meanwhile Rotom-Frost gives Torterra some defensive support in return by acting as an Ice resist that can pivot.
---Teambuilding Weaknesses---
This core greatly appreciates a partner or two that offers a way around Fire types, as a Fire type attacker holds the capacity to do immense damage to both Rotom-Frost and Torterra. Incidentally, using Occa Berry on Torterra reduces this weakness, allowing a player much more security in only using one Pokemon to circumvent Fire types. Special attackers that can threaten both Rotom-Frost and Torterra are also a concern, particularly Simipour.