If you want your very own Reaper King, Here's what you'll need to do:
-Hunt down a Reaper Queen and get it's heath to below 2000. The easiest way to do his is a trap. When the Queen begins to grow red, it means she's willing to transfer a symbiote to you. Aproach her, and a cutscene will play. After the cutscene has ended, you'll have an Offspring Buff with a countdown timer.
- You now have until the countdown ends to gather as much co as possible. The amount if co you gain determines what level your Reaper King will be.
-Make sure to stock up on Pheromone Glands! You'll need them to truck the baby into thinking you're its mother. If you don't have any, it will attack you.
-Once the baby is born, is will run around, VERY quickly. It won't stop until it kills something. I would suggest building a small room (2×2 maybe?) and to have something for the reaper o kill. Make sure to consume the Pheromone Gland before the baby is born.