Beat Brick as Lilith

I recently bought this game with my friend and we really enjoy duels, however I can't find way to beat him. What would be the best way and build to use against Brick? His berserk seems to be unstoppable with mass HP. I'm focusing on SMGs with my character(Lilth), though we're both on level 18, so it may change on higher levels.

Simplistically speaking, you'd defeat him if you had better gear and Dazed him (and stayed away from his Berserking). Siren PvP builds do not need to change per class faced; (of the two best PvP COMs) the build is your preference for how you wish to fight.

I was about to answer this question with advice for a Berserker (Brick). Beat a Berserker as Lilith (the Siren)? Excuse me, but ha! It's usually the other classes that seek advice to defeat the Siren. It's about time I wrote something like this for the Siren. [Edit: I forgot I already did.] Where do I even start? I'm going to write as a general PvP guide for Sirens.

Dazing
"I know there are a lot of people who think daze is OP in pvp. Which is true[.]"
Luckily, the Siren has three ways to Daze (for days). But wait, what is Dazing?

Dazed enemies behave normally, but suffer greatly slowed movement speed and reduced accuracy. The effect further extends to any weapons used by the Dazed foe, reducing the rate of fire of even fully automatic weapons, and slowing projectile velocity.

• Lilith can daze enemies with melee strikes, her action skill, or gunfire.
  • Striking
  • Dramatic Entrance
  • Mind Games
• Brick can daze enemies with melee strikes.
  • Bash

So, particularly if your Berserker opponent is smart enough to Sting like a Bee, do your best to keep your distance from him (until you wish to land Striking or Dramatic Entrance).
With Mind Games, the higher the rate of fire, the better (keeping accuracy constant of course). Dramatic Entrance doesn't always land at point blank. Striking can make up for that.

Silent Resolve
King (damage resistance).

High Velocity
Get this skill, at least when you get to the point where a player is downed in less than a second.

Phasewalk
Soldier's got Scorpio Turret, Hunter's got Bloodwing, Berserker's got Berserk, what do you got? Phasewalk, baby! Elemental explosions on entrance and exit, enhanced speed, invisibility, invincibility, surround sound, high defini—ahem. Want to Daze? Pop it. Health low? Pop it. To close the gap? Pop it. Others can hear your footsteps and the ambient noise, so end it fast to reduce the time they get to pinpoint you or end it late after crawling (crouched) around (to silence foot-falls) so that, even though they can tell you're nearby, your final position is unknown.

https://www.youtube.com/v/AcmpjIfb0OQ&autoplay=1&start=19&end=21 https://gaming.stackexchange.com/a/113632/46216

Radiance
Do not get this skill. "[I]t gives away your position in Phasewalk. I don't think that Radiance even damages other players in PvP."

Phase Strike & Venom
Don't get these either. Ever.

[A]t the upper levels/end-game...
Mêlée is negligible. This is a case of linear mêlée damage, quadratic bang bang. Although mêlée damage may not necessarily scale linearly, it's still bringing a knife to a gun-fight. At the upper levels, you should only use your mêlée attack offensively if you know the enemy's health is low enough that it will finish them off and you need to reload. Or it's a single enemy, but with a lot of health, and you've got Bash, so you want to Daze them to mitigate their damage output."

Slayer
There are no critical hits in PvP.

On-kill skills
At best, you get lucky somehow or you kite or have a car handy that you destroy right before duelling.

Mercenary COM
Anarchy or (Double) Stinger.
Gasher? Wildcat? Tsunami? https://www.youtube.com/v/qH5X_YtP5RU%26autoplay=1%26start=555%26end=557

Tempest COM (with +84% Shock Chance Resistance & +4 Silent Resolve)
Use with S&S Orion, shock S&S Thanatos, shock Redemption, or Undertaker, (or burst-fire rocket launchers (not so much in arena)).
You should be using shock grenade mods regardless.

"One-shot."

I've dabbled in Defender and Catalyst COMs. Defender COM was probably either to sandbag or get kills via grenade mod. Catalyst COM is for extended and/or consecutive rounds, for more Phasewalk, which is very important. Switch to it after a hit-and-run to recharge Phasewalk faster. Plaguebearer COM for Inner Glow.

Element
"Shock is the king element in PvP. This is because a player's total hit-points are mostly composed of shield."
"In PvP, you should always be using a shock artifact. Fire is lowest tier element because it does the least damage against shields." 

You can also study up on your opponent's strategy.