You can only activate “Grand Finale” once per every 3 long rests. It can only be activated when the character is downed/killed. When activated, hp returns to full, and all stats double (charisma, wisdom, AC, HP, etc.). Certain effects will  will happen to certain species of Ancient Dragons. When the battle is over, return the character back to normal, and have it’s HP turns to 1.

Crystal Ancient Dragons: any crystals fired will split into four, causing 1D4 damage if they hit. Ten can be fired as 1 action.

A small crystal that’s of your character’s Gem color fires from the user’s mouth. It does 1D6 piercing damage, and goes up to 30 feet. Will instantly disappear after 30 feet.