Best legion build?

Currently running Ruin + Undying + Thanatophobia + BBQ and it's a damn dirty build on its own but throw on Iridescent Button + any other preferred add-on and now you're really rockin. Sometimes I swap BBQ for Discordance as well, and/or swap out Undying for for Surge.

Overall this build gives you a lot of info and ability to keep the survivors working hard for very little gain.

First, Iridescent Button: This is gonna worry and confuse the survivors the entirety of the match with your map-wide terror radius. Feral Frenzy already gives you a loop advantage but on top of this, you're gonna destroy every pallet you vault, shutting down that loop forever.

Thanatophobia: Everyone being good and injured as Legion is so good at doing is gonna make them work harder to mend, harder to cleanse, harder to repair, etc... This helps protect your totems a bit too by giving you more time to get over and stop a cleanse, or chase people off gens and allow Ruin to work its magic.

BBQ: Obviously, information is king. Hook someone, get a glimpse at where everyone else is, allowing you to protect a gen, your totems, and of course make more people bleed.

It's not foolproof obviously. Top skill players expect bbq and can counter it. Most players will also remember to test for Ruin as soon as they get on a gen, and if it's there, they'll hunt for totems. So, this build potentially can leave you with just 1 beneficial perk, which is why i sometimes swap in Surge and/or Discordance.

Ruin+Undying goes better with legion with wasting time mending. Then you can stick with Enduring+Spirit Fury or keep Enduring and toss on Thanatophobia.

A lot of good builds mentioned already.

I personally use Corrupt, PGTW, BBQ, and Thanatophobia.

BBQ + Disco + Thana (this can be swapped out for something else though) + Ruin

Disco and BBQ obviously serve the purpose of having some intel and BP. Disco also gives the benefit of being pretty good for assuring some value out of FF, though it will also be quickly identified by keen minded Survivors. That said, I tend to approach generators looking slightly sideways to throw off Spine Chill, which can cause some confusion and question as to whether or not I'm running any intel perks. Thana and Ruin serve as slowdown. Thana also hopefully gets Survivors to waste time healing, and if they don't, they will be doing slower gens while being a 1-shot.

Enduring + Spirit Fury is a pretty good combo on Legion, and I totally get using it. In my own build, I'd swap Thana for Enduring, though I'd likely keep the rest. I like having some built in slowdown and some intel. If I had to use both, I would swap out Thana and Ruin since End+SF would give me more chase pressure, which reduces the amount of gen slowdown needed. I'd keep intel perks in order to ensure I can quickly get into those chases, and get some value of out of FF by crashing any gen parties.