|It increases damage dealt and taken.|
Harm is an ego that can appear on scarves and artefacts. It amplifies the damage dealt by the player by 30%, but also amplifies the damage received by 20%. This effect applies to all forms of damage, including torment. The damage is increased after AC and resistances are applied.
Up to 2 sources of Harm can stack. With 2 sources of harm, you'll deal 45% extra damage, but take 30% more damage.
Harm is an extreme double-edged sword. Even though you get a proportionally greater boost, there's many situations where you won't be attacking, but monsters will. Melee characters will be pelted from afar, casters are squishy enough already, and anyone won't want to be caught with Harm while trying to escape. You might kill thousands of monsters, but it only takes one particularly bad situation in order to kill you - or, at least, force item usage.
The damage boost can't be denied, though. Casters and ranged fighters who rely on killing enemies before they get to you should at least consider it. But since a mob of dangerous monsters will most likely outdamage you, Harm remains dubious for characters who don't need killing power.
Overall, harm is risky on the player level - if you are not prepared to disengage from fights early, then you are likely to die.
- Prior to 0.30, Harm couldn't stack.
- Prior to 0.25, Harm appeared on amulets of harm, which would drain the wearer upon removal.