Critical Mass Meltdown

You unleash a violent nuclear shockwave centered on yourself. Every other creature within 20 feet of you must make a Constitution saving throw. On a failed save, a target takes 4d8 Fire damage and 4d8 Radiant damage and is knocked Prone. On a successful save, it takes half damage and isn't knocked prone. After the explosion resolves, your hit points immediately drop to 0 and you begin making death saving throws.