the build to beat hard with all the classes.

MUST:
-Radiation tree: tons of dmg and extra helpful if you have high attack speed (only the top row)
-Flashbang star: Only the top row (bottom one optional for more survivability)
-Bulk Rounds Tree (full)
-Quick Draw Tree Tree (full)
-Swiftness (light magnet)

You want to build the full tree of the following
-Bulk Rounds Tree: for dmg

-Quick Draw Tree Tree: for dmg (make sure to not rush the one that gives 50% attack speed or you will lack dmg

-Flashbang Star: to be able to kite + protection (also combos with radiation)
-Gleam/Spotlight (I prefer gleam since is more reliable plus the blink but you as you wish)You can build it mid/late game. You can build whatever upgrade you need, personally I like to go 2 or 3 points on the top row so I get light wave to pick the exp next to the upgrade that gives exp once revealed.

Half tree:
-Swiftness (light magnet) To pick up the exp and the movement speed helps with the other upgrades, which some of them decrease your overall mov. speed

Optionals
-Shield, just to be safe, build the bottom row so you get the stats, the extra 50% visibility which synergizes with this build and the akimbo to shoot from the back.*Billy "ShootYouInTheBack" Bobby*
Others at your own discretion, but pretty much with bulk rounds, quick draw, flashbang and radiation you're set, you only need vision to proc the radiation and pick up the exp (flashbang does that but not totally reliable)
e.g. at late game is kinda helpful to put 3 or 4 points on it to beat the final boss and the mobs that have high hp, don't prioritize this. Alternatively, you can build shield and build the bottom so you get stats from it.
End build example:

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