Hitting an enemy gives them 1-4 stacks of 2.5% Brittleness. Debuff lasts for 5 seconds and can have a maximum of 16 stacks.
Critical hit chance scales by your current heat level up to 27.5-50%. Also increases critical ranged attacks damage by 4-10%.
Target receives 1-4 Stacks of 2.5% Brittleness on direct projectile hit. Debuff lasts for 5 seconds and can have a maximum of 16 stacks.
Example build for Karnak Twins Hard Mode guide: https://steamcommunity.com/sharedfiles/filedetails/?id=3115826337