Focus Crystal

The Focus Crystal is an item introduced in Risk of Rain 2.

Hitting an enemy within 13 units of the character will apply a 1.15 (+0.15 per stack) multiplier to the damage dealt.

The 13 units are measured as a sphere around the character.

This item is extremely powerful to stack as Mercenary, Loader, and MUL-T since most of their attacks will fall within the 13 unit range of the Focus Crystal, meaning that it is essentially a consistent damage buff. Most other characters will be attacking from far outside of the activation range, however, so it is advisable to treat this item a bit like Bustling Fungus in a way if you have any of these characters playing with you in multiplayer.