Neuvillette

5★

HydroCatalystMain Damage

TL;DR

Neuvillette holds down the attack button and a river of water comes out for three seconds. That's the character. His Skill and Burst are there to leave little water droplets floating around him, and the charged attack pulls those in by itself, which starts the river almost instantly instead of after a slow wind-up. Stack Max HP and Crit, stay near the droplets, and don't worry about anything else.

Rotation

Set up your supports first.
Skill (E) for droplets, then hold attack for a full charged attack.
Burst (Q), then keep holding attack. Stay near the droplets rather than chasing enemies away from them.
Aim for three or four charged attacks per rotation, then reset.

Abilities

Charged attack	Hold the attack button. A continuous beam of Hydro for about 3 seconds that costs no stamina. This is where all of his damage comes from.
Skill (E)	A short waterfall that does some damage and, more importantly, leaves three water droplets floating nearby.
Burst (Q)	Big AoE Hydro damage with a delayed second half, and six more droplets. Cast it for the droplets as much as the damage.

The one mechanic to understand

Droplets are the whole loop.

Without droplets, the charged attack takes about four seconds to wind up before the beam even starts, which is far too slow to use in a fight. Absorb up to three droplets and that wind-up drops to about one second. The beam also drains his own health while it fires, and the droplets heal that back, so absorbing them solves both problems at once. You don't collect them yourself. They hang in the air where his skill and burst left them, and holding the attack button drags any that are close enough straight into him. All you have to get right is not wandering off from where you cast.

Neuvillette casting his skill, leaving three glowing blue droplets hovering in the air around him — Glowing blue orbs at about shoulder height. Start a charged attack while they're that close and they get pulled in for you.

What actually matters

The two or three real decisions. Everything else is noise.

Max HP is his attack stat. All of his damage scales off it. HP sands, HP substats, and Crit on top.
Teammates who cause Hydro reactions. Each different kind of reaction your team triggers stacks up a damage bonus for him, up to three stacks, and three stacks is a very large multiplier. It's why he's never played solo Hydro.
Energy Recharge barely matters. Around 110% is plenty, which is unusual for a 5-star and makes the rest of the build easy.

Gear

A build that works. KeqingMains lists every other option.

Weapon	Max HP, then Crit. Prototype Amber is craftable, has an HP main stat and heals and gives energy on burst, which covers his two small weaknesses at once. It is a serious pick, not a placeholder.
Artifacts	4-piece Marechaussee Hunter. It boosts charged attack damage and gives him a big pile of Crit Rate whenever his health moves, which the beam's self-drain triggers constantly.
Main stats	HP sands, Hydro goblet, Crit circlet. An HP circlet is fine too if your Crit is already sorted by the artifact set.

Works well with

Dendro

Electro

Cryo

The point of these is variety, not raw power. Three different kinds of Hydro reaction in one team is what maxes out his damage bonus, so a mixed team beats a specialised one here.

Don't bother

Normal attacks. Hold the button, don't tap it.
Attack% anything. HP is his scaling stat and Attack does effectively nothing.
Stacking Energy Recharge. He needs very little of it.
Panicking about the health drain. It stops below half health, and the droplets heal it back anyway.

Want the full theorycrafting version? Read Neuvillette on KeqingMains.