Enhanced Rasengan

You create a swirling sphere of force energy in your palm. Make a melee spell attack against the target. On hit, the target takes 4d12 force damage and 3d6 damage of your choice between bludgeoning,  slashing, or piercing, and must make a constitution saving throw. On a successful save the target takes half of the roled damage and isnt knocked back. On a failed save the target takes the full damage, and is flung back 25 feet.

This spell's damage increases by 1d12 and 1d6 and the knock back increases by an additional 5 feet for every spell slot used beyond 3rd level.