Symbiote (Men in Black)

Symbiotes are a sapient species of amorphous creatures which form temporary symbiotic associations with other life forms. They are notable for their extraordinary abilities, which include shapeshifting and healing themselves and others.

Biology
In their natural state, Symbiotes are limbless slug-like creatures which cannot survive on their own for long. To remain alive, they need to merge with a host. When merged, the Symbiote takes the form of a second head protruding from the host's neck. After 20 hours, the merge becomes permanent, and thus host and Symbiote transform into a single being and can no longer be separated. To avoid this undesirable fate, Symbiotes prefer to change hosts every few hours.

Merging with a Symbiote gives the host access to the Symbiote's abilities, such as shapeshifting and fire-breathing. A Symbiote can stretch and alter their host's body in ludicrous ways, and regenerate any kind of injury, including being blown to bits, thus essentially making both the Symbiote and the host indestructible while merged. Merging with a Symbiote heals previous injuries of the host instantaneously, and Symbiote hosts can also heal other creatures by touch.

Appearances

 * Men in Black: The Series
 * s01e07, "The Symbiote Syndrome" (1997)
 * s02e16, "The Heads You Lose Syndrome" (1998)
 * s02e19, "The Jack O'Lantern Syndrome" (1998)
 * s02e22, "The Fmall, Fmall World Syndrome" (1998)
 * s02e26, "The Blackguard Syndrome" (1999)