Zhongli is best as a Support unit, creating shields to protect your primary DPS characters while still dealing lots of damage even when he’s off-field. There’s a few ways you can go about building him to match your play style.
In general, you want ATK%, Geo DMG and Crit DMG as your main stats. HP% can be a nice bonus, since Zhongli gets an attack bonus based on his maximum health at higher Ascensions.
Zhongli Artifacts: Shield Support
4 Archaic Petra
While Zhongli makes shields, the shield-centric Artifact set Retracing Bolide isn’t that useful since the effects only apply to the wearer. The same Domain of Guyun where you get Bolide from is also where you get Archaic Petra, the premier Geo set. A four-piece set gives everyone a 35% damage bonus when picking up a shield from an Elemental Shard for that element.
Zhongli’s Skill, Dominus Lapidis, creates a shield while also produces a Stone Stele that does a burst of AoE Geo damage at creation. This is a quick way of Crystalizing, giving a reliable and fast way of triggering the Archaic Petra ability. Zhongli needs to pick up the Shard, so you’ll have to inflict an element and then switch to Zhongli. Switch back and you’ll have the buff from Archaic Petra and your enemies will have the Res debuff from Zhongli’s ability.
Zhongli Artifacts: Burst Support
2 Archaic Petra / 2 Noblesse Oblige
Zhongli’s Elemental Burst Planet Befall is quite powerful, dealing heavy damage while Petrifying enemies. Two pieces of Archaic Petra gives a 15% Geo DMG bonus, and Noblesse gives a 20% bonus to Elemental Burst DMG. Noblesse Oblige can be found in Clear Pool and Mountain at Mt. Aozang.
This fight is tough, since you fight one of each kind of Abyss Mage. A trick I’ve found is that right after activating the challenge, run to the corner of the room so you don’t aggro the Hydro or Cryo Mage. This will let you more easily deal with the two enemies, and you also won’t be juggled by being frozen.
4 Gladiator’s Finale
If you want him as a DPS unit, you can stack a simple four-piece set of Gladiator’s Finale to up his raw Attack stat. You get Gladiator’s Finale Artifacts by defeating Bosses.
Weapons will vary based on what you have, but Zhongli can be flexible with what weapon you give him. His best weapon is the Spear of Homa, but it’s an Even Wish exclusive five-star weapon so most players won’t have that. Any of the five-star Polearms will be fine on Zhongli. You’ll just get more style points for using the Vortex Vanquisher.
The Battle Pass reward Deathmatch is just an all-around great weapon. Favonius Lance lets you get his Burst ready faster.
For free-to-play friendly options, either of the craftable Polearms work well on Zhongli. Crescent Pike bumps up your Physical DMG and increases Normal and Charged attack after picking up an Elemental Orb or Particle. Prototype Starglitter increases Energy Recharge and gives a damage buff when using an Elemental Skill. The one you want will depend on who else you have on your team.
Weirdly enough, the three-star Black Tassel isn’t awful. It has low base stats and a mostly useless ability, but it has a HP% as a secondary stat. It basically acts like an Artifact as a weapon to take advantage of Zhongli’s passive HP based Attack buff.