Power Keg Engine: Crit Scaling + Low CD Burn
Pulling off a successful Powder Keg victory requires a lot of things, but the two main parts of your engine are Crit% Scaling and maximizing your Charges from Burn sources.
Reaching 100% Crit is essential because it upgrades your Keg from doing 50% of you enemy's Max Health to doing 100%.
This will allow you to straight up one-shot certain matchups that lack defenses. If they survive, the initial blow, your Burn can usually finish the job (they are also scaling from Crit).
Note that this build does better against Heal/Health-stacking based comps but can struggle in Shield heavy metas. This is because Shields reduce Burn damage by 50% and because your Keg can't do much against a comp that relies on high shields but doesn't invest a lot into Max HP.
Crit Scaling
Star Chart was the perfect fit for the build as it increased Crit Chance and granted a huge 25% Cooldown reduction to the Keg.
Star Chart (Crit% + Cooldown Reduction)
Vanessa's Amulet and Inexorable were the other two major players for Crit% scaling and offered it to the entire board. Finding Inexorable ASAP is pretty key to making this build work (Rarran found it Day 3).
Vanessa's Amulet and Inexorable (AoE Crit% Increase)
Low CD Burn
While you increase your Crit%, you're going to also want to find sources Burn that can cast ASAP.
Lighter is a classic option but a crucial find is Heated Shells, a skill that turns Ammo use into Burn activators.
It unlocks new sources like Nesting Doll while letting you double dip with items like Pop Snapper that have both Burn and Ammo.
Lighter (fast-casting Burn)
Heated Shells (Skill that converts Ammo use --> Burn)
Nesting Doll (Offers defense while proccing Heated Shells)
Pop Snappers (double dips Burn + Ammo)