Blast of Stored Power

You gather energy in your body for the duration of the spell. When the spell ends, either because you choose to release it at a creature or lose concentration, the energy explodes in a burst of force. However, upon losing concentration, you risk taking 4d10 force damage yourself. While gathering energy, your movement speed becomes 0, you cannot benefit from buffs to your movement, and you gain resistance to all damage types except psychic damage.

The spell's base damage is 6d10 force damage, and at the end of each turn while concentrating on this spell, the damage increases by 4d10.

As a free action during your turn you can release the energy stored up within you, dealing damage to the targeted creature.

(Credit to @Micramism on discord for helping me write this because I'm a complete beginner lol)