Shell Boss Killer

This build is designed to one-shot bosses and mini bosses, I usually run this with at least one friend who can deal with general room clearing while I deal with elites to off set his lack of aoe, but you can still make it work if you're good at dodging.

Also his ult is just there for the ad% increase, I wouldn't invest in it too much once it gets past 50% as you can scale better by investing elsewhere or by swapping it our for something that scales with AD like Stygian rush or shout of oblivion (if you don't mind fighting hunters for it).

Priority picks
S tier finds: Obsidian - Stygian Rush - Vile Strike - Voracity - Wind - Swift Strike - Void - Confidence - Finality (only on stygian rush)
A tier finds: Ice claw - Teal blade - Responsibility (S tier with stygian rush) - Static overdrive - Lightning dance - Blade storm (for aoe) - Composure

Playstyle
If you manage to get Stygian Rush you are set to completely nuke bosses as Shells crazy high ad scaling once you invest in his passive a bit and adding on multiplicative damage boosts (lethality, confidence, finality) make for an easy one shot build. Even a mid build will still chunk a boss for a lot and you can finish them of by spamming dashes and attack resets most of the time.

I like to have at least one dash ability that has a super low cooldown, either naturally or through essences like efficiency, metal, obsidian, and momentum, as it basically acts as another dodge and helps with his room clearing issues, also slapping something like regeneration helps keep you healthy. Aim to kill the highest enemies first and use blue laceration to take out all the little guys chasing you.

No essences on Laceration because you can kinda just use whatever you want, it's there for the utility of either extra dash or invulnerability + aoe. Wouldn't recommend using it as your main damage source as it's hard to consistently use the dash portion and blue laceration only helps as aoe dps wise.

Also since I can't mess with flex slots on this site I like to run Valiant challenger and Perceive, Learn, Adapt in 2 of his flex slots.