Gambling Addict is a primary ability.
When you attack something with this ability, there is a 30% chance you deal 35% more damage, and a 70% chance you deal 15% less damage.
This averages out to where you deal the same amount of damage over time, but when someone is low, you could get lucky and kill them, or unlucky and they survive.
Obtaining
You get this ability with the Gambling Addict advancement, which you get by opening 20 ominous vaults.