Doubt

Doubt is a Curse card that is Unplayable and applies 1 stack of Weak to you at the end of every turn it is in your hand. Weak reduces your Attack damage output by 25%, making each stack of Doubt drawn a meaningful offensive debuff for that turn. While Weak wears off (1 stack per turn), the continuous reapplication from Doubt whenever it’s drawn ensures that it consistently hampers your damage in fights where your deck cycles frequently. It has no upgrade.