Wounds up to X units in a line across from this unit (FRONT ROW first, then BACK ROW).
Every point of Defense a unit has will block one Fireball. Every unit wounded by Fireball will use up one Fireball.
Fireball will first try to hit the FRONT ROW unit across. If successful, it will use its remaining Fireball to hit the BACK ROW unit across. Only those two units can be hit.
If there isn't a unit in the FRONT ROW across, Fireball will not waste a point trying to hit it.
9 units have the Fireball ability: