Beast Within

Target creature within range makes a Constitution saving throw. If it fails, it takes 10d6 Necrotic damage from internal injuries and a horrific homunculus of pure green mana bursts forth from its midsection. The resulting Beast usually resembles an eyeless crocodile with parts of its skeleton and jaw exposed to the air.

The target takes an additional 3d6 Necrotic damage at the start of each of their turns until they benefit from any kind of magical healing or the Regeneration spell, as the massive open wound in their midsection continues to bleed. 
If the target succeeds on their saving throw, they instead take half damage with no other effect. 

The Beast summoned as part of this spell appears in an unoccupied space adjacent to the target and has hitpoints equal to the damage dealt to the creature that hosted it as part of this spell.
If there is no unoccupied space adjacent to the target, they take only the initial damage and the remainder of the spell fails.
The Beast rolls initiative as soon as it appears and attacks the creature that hosted it until one or both perish. Once its original target is slain, it defends itself and takes no other action.

After one minute or if you lose concentration, the Beast perishes as it dissolves into muck.

  At Higher Levels. When you cast this spell using a spell slot of 6th or higher level, the initial damage increases by 1d6 for each slot level above 6th.