Parasited - Little Puck [best] -

By "parasiting" Little Puck, the Grief Eater allows him to live out a fantasy. Every "upgrade" the parasite gives (claws, camouflage, wall-crawling) is actually Puck’s body shutting down further. The final level—where Puck merges permanently with the shadow—is actually the moment of brain death.

: She succumbs to the parasite and emerges from a human-sized cocoon as the , covered in dark veins and slime. Parasited - Little Puck

However, if you're looking for a title that implies Little Puck has been affected by parasites, the most grammatically correct and attention-grabbing option could be: By "parasiting" Little Puck, the Grief Eater allows

: Sickly kittens are often "infested" with fleas. Useful treatments include: By "parasiting" Little Puck