Runestones will change the way a skill operates, adding secondary effect such as stunning or an increased area-of-effect radius. They'll come in five different colours, each affecting every skill in a different way. Runestones will also have power ranks, applying more intense effects the more powerful the stone is.

A Golden Runestone applied to the Sweeping Wind skill, for example, will make it increase the monk's Spirit regeneration. An Obsidian Runestone, however, would cause Sweeping Wind to also create a whirlwind around the monk, damaging enemies who touch it.

Runestones will apply different effects to different skills, too. While an Obsidian Runestone applied to the demon hunter's Cluster Arrow skill will make it rain grenades, on the witch doctor's Acid Cloud it'll spawn slimes to attack nearby enemies.