Undertow v2

You launch into the air diving down onto enemies below with deadly force. You teleport up to 10 feet to a space you can see. Each creature in a 10-foot-radius square centered on the point where you land must make a Dexterity saving throw. A target takes 6d8 slashing damage on a failed save, or half as much damage on a successful one. If you kill a creature with this spell you gain the ability to cast it once more as a bonus action dealing 3d8 slashing damage. 

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At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d8 for each slot level above 3rd.