Arcane Mine

You create a hidden mine, an orb of invisible arcane energy which floats gently above the ground until something touches it, which causes it to explode. Two arcane mines can never occupy the same space, if two mines touch, they both explode. You cannot float arcane mines in midair, 5 ft. or more above a supporting surface (unless you use another spell or device to do so).

When you cast Arcane Mine, each creature which can see the mine’s location gets to try a DC 15 test of Seeking or Spellcraft to detect the mine.
A creature which is not aware of the mine must pass a DC 15 test of Seeking, Spellcraft, or use some other means for the mine to be revealed to them.
You may choose to make your mines plainly visible as a fast action.

If a creature enters a space that has a mine in it, the mine explodes, damaging everything within a 5 ft. burst of the mine (affecting the space the mine is in and all adjacent spaces). Each affected creature gets a health save to half the damage. If this happens in the middle of a creature’s movement, the mine interrupts their movement and explodes, and then they may choose to stop or keep moving. Mines only explode once and are destroyed in the process.
Mines placed in an occupied space detonate instantly.
As an action, any number of your mines can be remotely detonated with a snap of your fingers.

Arcane mines are quite unstable. Touching them is not the only thing that can set them off. If they are disturbed enough, exposed to sufficient trauma (such as an attack), a high concentration of arcane energy, or mundane fire or lightning, they may explode.

While Arcane Mines is a hostile ability, it is subtle, and placing Arcane Mines does not break Invisibility or cause its caster to become unhidden. The caster remotely detonating them does.

Subtle:
Casting this spell while hidden does not cause you to become unhidden.

Suggested Backfire: The mines appear on spaces of the Headmaster’s choosing. You do not know where they are, cannot make them visible, and cannot detonate them.

Affinity:
When you take this class, choose which element your Arcane Mines are.
Whenever you cast this spell, it will normally be of that element.
You can try to cast this spell using a different element, but must pass a DC 20 test of Spellcraft each time to change the element from what it normally is.

(You may Intensify every mine explosion).

Incompatible: Dilute and Concentrate from Advanced Geometry.