Need help with brainstorming...

I'm designing an alien race for one of my stories and could use some help.
In the story, the MC is a clone that was recreated with the intent of harvesting an alien breed that procreates by gestation within a host.

Hi Lavender, I'll try to help.

Maybe it could be a parasite that derives oxygen, nutrition and moisture by sprouting tendrils that hook into and meld with the central nervous system and spine, and releases it's progeny as spores by injecting them into the waste system of the host.

Hmmm… maybe. I was thinking a sentient race rather then parasitic though.

Oh.

Maybe a quantum race that imprints itself on the person's skin in 2D, but can "unfold into 3D like normal creatures.

Huh?

Oh wait, I get it!
Not quite.
I was thinking it was something that implanted a larvae (or some equivalent) into a host and incubates in it until it hatches.
I'm just not sure what it should look like.

Okay, let me rephrase (sorry I am really tired) it's humanoid, but requires a host for procreation.

Then maybe the larvae could be the parasite I mentioned earlier, but it detaches from the host, losing it's tendrils to become an embryo thing that RAPIDLY matures into an adult or adolescent.

As for what it should look like, maybe a hairless, spindly humanlike thing with a prominent or differently shaped braincase and ridges on the back and head.

Ooooo. Thanks for the suggestion!

I'm great at worldbuilding. These things come naturally to me.

The rule of cool, obviously.

In all seriousness, mutation and evolution could help it fight off the ways humans have to deter it, at least until humans develope sufficient enough means to do so.