I

Headshot Booster

Great for early poking.

I

Extra Health

Great hp increase and builds into Fortitude.

I

Rapid Rounds

Slight DPS increase and builds into Swift Striker.

II

Swift Striker

Significant dps increase pretty much required on Gun Warden.

II

Active

Fleetfoot

Really nice to have on Warden.

II

Active

Slowing Hex

Helps you secure kills easier, Binding word is easier to hit and stops enemies from escaping.

I

Restorative Shot

More weapon damage while increasing sustain.

II

Active

Guardian Ward

Good for playing more aggressive in lane and gives a decent move speed boost too.

IV

Glass Cannon

Almost doubles your DPS. Try to build stacks after buying this.

III

Fortitude

Significant HP increase and you almost never have to heal in base.

III

Trophy Collector

Good if you can get stacks easily or if its a long game. Preferably bought in place of Enduring Speed.

IV

Siphon Bullets

Makes you tankier and increases your damage slightly.

IV

Spellslinger

Pretty good on Warden. Personally I don't like it.

IV

Lucky Shot

Significant DPS increase. 25% chance to do 2.25x damage is huge.

IV

Armor Piercing Rounds

Anti-Plated Armor / Bullet Resist.

IV

Ricochet

25% Firerate is really good. Also insanely good in teamfights.

IV

Silencer

Strong against ability/spirit builds. Builds up easily with Warden's Gun and works with Ricochet.

IV

Inhibitor

Wins 1v1's and Great in teamfights if combined with Ricochet

III

Counterspell

You can parry ults with this.

III

Active

Debuff Remover

Useful for removing crucial stuns and strong DoT.

IV

Plated Armor

Better than Bullet Resilience reduces on-hit effects too. (Haze passive, Toxic Bullets, etc.)

IV

Active

Divine Barrier

Stronger debuff remover and gives 600 barrier. But can't remove stuns. (or ults)

IV

Cheat Death

Helps you keep your Glass Cannon stacks. also good for avoiding unnecessary deaths.

III

Toxic Bullets

Bleed + Antiheal. Great against tanks.

I

Monster Rounds

Easier to farm and take down objectives faster.

III

Active

Cultist Sacrifice

Even more objective damage and good stats.

II

Slowing Bullets

Helps you hit shots easier.

IV

Lightning Scroll

Strong with Warden's ULT. Helps you deal more damage and you get easier shots on them while they're stunned.

IV

Active

Curse

Useful for stopping ults and making someone useless.