Artillery Siege

Artillery Siege is a spell meant for sustained long range bombardment in order to cause destruction of an enemy encampment. The spell has high damage and destruction potential, though it leaves its caster vulnerable to attack. This spell is only accessible through specialized training for artillery mages for military purposes. 

After heavy concentration and ritual casting, the caster may enter into an artillery siege stance for 1 hour. The caster is unable to move from the position or cast any other spells/perform any other action, even spells that do not require concentration. The stance ends when concentration is broken, duration is up, or the caster chooses to end the spell. The caster then ends into a weakened state, halving movement speed and unable to cast any spell for 10 minutes. The caster can cast this spell once per long rest.

Artillery Siege stance - Enables the caster to cast artillery shell, minimum range of 500 ft. A blazing ball of fire and iron swarms slowly into existence until it reaches 5 ft in diameter, taking 5 minutes to form. The caster then chooses a distance and direction. The shell launches in a parabolic arc, the highest point 1.5x the distance it travels, and travels at a speed of 1 second per 100 ft. The shell produces bright light and a loud scream, and those who view its initial launch can estimate the casting location. 

The shell explodes upon contact with a physical or magical barrier at least 5 feet in diameter. Each creature in a 30-foot-radius sphere centered on the point the shell lands must make a Dexterity saving throw. If a creature is within 10 feet of the point of impact they fail the automatically. A target takes 10d6 fire damage and 10d6 bludgeoning damage on a failed save, or half as much damage on a successful one. Structures within the radius take maximum damage and are set on fire. 

The fire and explosion ignores cover such as walls and ceilings. If the shell impacts the ground, it leaves a crater 5 feet deep and 10 feet in diameter. Creatures below the ground with at least 5 feet of material separating them take no damage from the shell, though any tunnels or caves are at risk of collapse. 

At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, the duration of artillery siege stance increases by 1/2 hour per spell level.