Aivoc's Energy Beam

You channel an energy beam, recycling the discarded elemental energies around you. You must channel this spell for at least three rounds, meaning you must reach the start of your turn three times after the casting of this spell. While you are channeling, you're concentrating on this spell, your speed is 0, attack rolls have advantage against you, and if you are hit by an attack, it is automatically a critical. If you cast a spell other than a cantrip before this spell is completed, or are moved from your initial position, then the channel stops. If the channel stops, then this spell is wasted.

Whenever an evocation spell is cast within 60 ft of you while you are channelling, you gain an energy charge.

On the third turn of this spell's channel, you can use an action to fire an energy beam. This beam must be acid, cold, fire, lightning, radiant, or force. You choose a point you can see within 60ft, and make a 60ft line from that point to another point. Creatures in the beam's path must make a Dexterity Save, taking 12d8, plus a d8 per energy charge, damage of the chosen type on a failure, or half on a success. This spell then ends.

If you don't fire the beam on that turn, you can maintain the channel and instead fire it on a future turn.