Runestones

Runestones are physics objects that can cause certain effects nearby when activated by the player. They can be found naturally in the world on small pedestals. Kicking a runestone will activate it, indicated by circles of magic particles emanating from it. Kicking it again deactivates it. The effects vary, but usually include modifying projectiles that pass through its area of effect. This affects enemy projectiles too, when applicable.

Trivia
Runestones can also be thrown and used for accidental kills in a similar manner as Emerald Tablets.