demons flame

you shoot a powerful large flame that does 10 d12 plus 8d6 fire damage plus 20 d4 thunders damage. when you hit level 18 and 19 it adds 8 d6 fire damage but when you hit level 20 you add 4 d12 and 10 d8 fire damage. this will take 3 spell slots and can only used 1 before a long rest (demon staff only needs long rest)