Taboo: More Than One Kind.

You transform all the gold in your hand into a single coin, which you then hurl at your enemy. After a few seconds, the coin multiplies uncontrollably, reaching into the thousands.
Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 10d6 bludgeoning damage on a failed save, or half as much damage on a successful one.

The coins produced by the spell spread across the area, turning it into difficult terrain. They vanish after 1 minute.
You can negate the damage you would take from the spell by using the Payback spell.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d6 for each slot level above 4rd.