You have access to...

1x Yv-666
3x Scyk
3x Kihraxz

Every upgrade card - but no other ship types.

You must use the Yv-666

What's the best build you can make?

Well here is my attempt. The idea is use the Yv-666 to support my Kihraxz Fighters. They should be able to take out one maybe two ships and then it's just a matter clean up. My thinking is also to give the YV-666 as many options for acquiring a target lock as possible.

https://geordanr.github.io/xwing/?f=Scum%20and%20Villainy&d=v3!s!133:-1,-1,133,-1,122,-1:24:3:;138:14,128:-1:-1:;138:14,128:-1:-1:

I feel like this is the obvious answer, but:

Trandoshan Slaver + Bossk + Gunner + Tactician

Cartel Marauder x3

That leaves 2 points, so maybe add Feedback Array on the Slaver to deal with those pesky aces that can get stuck on your tail.

I'll toss in an idea as well ) .

Razpberry Point Veterans.

Latts Razzi + Tactician, K4 security Droid, weapons engineer, Engine Upgrade, xx-23 s-threat tracers .
3x Tansarii Point Veteran + Crack shot

Latts will generate dual target locks each turn - so she can trigger her ability, on green moves, allowing Engine to help pull a full turn, or more than a turn to threaten the rear. Tactician also creates a stress zone that's fairly large. The Tansari's can alpha with TL + Focus and crack shot, with further agility reduction from Latts Razzi. Finally, all of the ships are P.S. 5 - so they have flexibility of movement, and can dodge lower P.S. ships - the movement and action economy is high enough to possibly drop a TLT carrier before they fire.

So, I've never used a YV before, but here goes...

Latts Razzi - Weapons Engineer, K4 Security Droid, Tactical Jammer

Serissu - Crack Shot, Stealth Device, Title, HLC

Tansaari Point Vet - Crack Shot, Title, HLC

Razzi drops agility and provides extra protection for the powerful but fragile Scyks. Serissu's ability additionally helps protect Razzi and Vet while Stealth Device helps protect Serissu. Between the lowered agility from Razzi, crack shot, and a 4-dice attack, the Scyks should be able to dish out some serious damage.

Latts doesn't have to worry too much about getting stressed thanks to the K4, the Weapon Engineer provides plenty of target locks, and the Cartel Marauders give a decent chunk of firepower and you can split one off to cover Latts' blind spot.

Well here is my attempt. The idea is use the Yv-666 to support my Kihraxz Fighters. They should be able to take out one maybe two ships and then it's just a matter clean up. My thinking is also to give the YV-666 as many options for acquiring a target lock as possible.

https://geordanr.github.io/xwing/?f=Scum%20and%20Villainy&d=v3!s!133:-1,-1,133,-1,122,-1:24:3:;138:14,128:-1:-1:;138:14,128:-1:-1:

I like this one a lot, but I think I'd drop the Hound's Tooth title to upgrade the Cartel Marauders to Black Sun Aces. Then I'd consider dropping Bossk to add Crack Shot to the Kihraxz fighters. With Latts, though, I really want to put Weapons Engineer on her. I don't know if it's better to hang onto Engine Upgrade, or drop it for Weapons Engineer. I don't get to open my YV-666 until Christmas, so I just don't know how necessary the boost is. I'd probably drop it, though and add the Engineer.

Latts Razzi (33)

-K4-Security Droid (3)

-Weapons Engineer (3)

-Inertial Dampeners (1)

Black Sun Ace (23) 2x

-Crack Shot (1)

-Glitterstim (2)

-Cluster Missiles (4)

It's nice having everyone at PS 5 for freedom of activation order. I don't think an initiative bid is critical in a list with PS 5 all around, so I added Inertial Dampeners to fill up the last point. You may think that Inertial Dampeners is pointless on a ship that can perform a stop maneuver, but I disagree. It can be easy to predict that stop maneuver, so when you think you want to stop, you don't have to lock yourself into that. You can do a turn or zoom full ahead and if you would be blocked, then put on your Inertial Dampeners and hold your position.

Moralo Eval (47)
YV-666 (34), Heavy Laser Cannon (7), K4 Security Droid (3), Recon Specialist (3)

Black Sun Ace (28)
Kihraxz Fighter (23), Veteran Instincts (1), Advanced Homing Missiles (3), Inertial Dampeners (1)

Black Sun Ace (25)
Kihraxz Fighter (23), Veteran Instincts (1), Inertial Dampeners (1)

soften em up with the BSA and finish them with M.E.