Reddit mentions of Evolutionary Wars--A Three-Billion-Year Arms Race: The Battle of Species on Land, at Sea, and in the Air

Nature is full of weird creatures that you could use for inspiration for your aliens.

Parasites are great examples, and can control their host or become a part of their mate:

https://www.youtube.com/watch?v=2irXpAMBHkE

https://www.futurity.org/fanfin-seadevil-fish-1713022-2/

Planarians have incredible regeneration abilities, which we can use to make 3 headed worms.

https://youtu.be/roZeOBZAa2Q

We can even transplant a piece of worm to another, and grow a worm in a worm:

https://www.alamy.com/the-biological-bulletin-biology-zoology-biology-marine-biology-studies-on-transplantation-in-planaria-iqi-formation-of-a-secondary-pharynx-in-the-posterior-region-and-of-reversing-the-polarity-of-the-region-originally-anterior-to-the-level-of-the-graft-this-reversal-of-polarity-is-shown-by-the-develop-ment-of-a-new-pharynx-opposite-in-direction-to-the-original-pharynx-and-by-complete-reorganization-of-the-alimentary-tract-it-may-also-inhibit-head-formation-at-the-cut-surface-several-millimeters-fig-ii-p-dorotocephala-with-head-graft-developing-on-the-ventral-surface-of-the-host-image234673061.html

You could find a lot of other examples in a book like this one:

https://www.amazon.ca/Evolutionary-Wars-Three-Billion-Year-Arms-Race/dp/0716737752/ref=sr_1_11?keywords=evolution+arms+race&qid=1557509637&s=gateway&sr=8-11