Seed of Destruction

This spell impregnates a living creature with a rapidly gestating hydra that consumes the target from within before emerging to wreak havoc on the world. Make a ranged spell attack against a living creature within range that you can see. On a hit, you implant a five‑headed embryonic growth into the creature. Roll 1d3 + 1 to determine how many rounds it takes the embryo to mature.

During the rounds when the embryo is gestating, the affected creature takes 5d4 slashing damage at the start of its turn, or half the damage with a successful Constitution saving throw.

When the gestation period has elapsed, a tiny hydra erupts from the target’s abdomen at the start of your turn. The hydra appears in an unoccupied space adjacent to the target and immediately grows into a full-size Huge aberration. Nearby creatures are pushed away to clear a sufficient space as the hydra grows. This creature is a standard hydra, but with the ability to cast bane as an action (spell save DC 11) requiring no spell components. Roll initiative for the hydra, which takes its own turns. It obeys verbal commands that you issue to it (no action required by you). If you don’t give it a command or it can’t follow your command, the hydra attacks the nearest living creature.

At the end of each of the hydra’s turns, you must make a DC 15 Charisma saving throw. On a successful save, the hydra remains under your control and friendly to you and your companions. On a failed save, your control ends, the hydra becomes hostile to all creatures, and it attacks the nearest creature to the best of its ability.

The hydra disappears at the end of the spell’s duration, or its existence can be cut short with a wish spell or comparable magic, but nothing less. The embryo can be destroyed before it reaches maturity by using a dispel magic spell under the normal rules for dispelling high-level magic.