Arcane Sigil

Using chalk you make a arcane rune on a surfaced object.

You inscribe it either on a surface (such as a table or a section of floor or wall) The sigil can cover an area no larger than 10 feet in diameter. If the surface or object is moved more than 10 feet from where you cast this spell, the sigil is broken, and the spell ends without being triggered.

The sigil is nearly invisible and requires a successful Intelligence (Investigation) check against your spell save DC to be found.

When triggered, the sigil erupts with magical energy in a 10-foot-radius sphere centered on the sigil. The sphere spreads around corners. Each creature in the area must make a Dexterity saving throw. A creature takes 3d6 acid, cold, fire, lightning, or thunder damage on a failed saving throw (your choice when you create the sigil), or half as much damage on a successful one.