X Parasites

The X Parasites are a creature from the Metroid series appear in Ye Olde Battle Royale, and are the main force used by boymonkey130. They exist only in the Movie, and their chief rival is Jacen's Sun Crusher. The only way to kill the X is through absorption or extreme explosion. They can copy the DNA of their host, and transform into a copy of it.

Ye Olde Battle Royale
Raynor Jayce Zeraph, when killed, is revealed to have an X Parasite inside him, which flies away. This turns into the RZX (Raynor Zeraph X), which from then on essentially "is" Raynor. (BR:1:13)

Raynor does this to Jacen, and transforms into a Ninja Pirate (BR:2:4). (I guess it's still Raynor. Don't ask.) Later, when confronted by Samus (who is under the control of Jacen at this point), he turns into the shape of presumably Adam Malkovich, which stuns her for long enough for him to transform into a mole, dig to the center of the earth, and use methods to produce thousands of X Parasites (BR:2:7). Part of this horde transforms into various Metroid bosses, lead by Mother Brain.

Eventually, they also assimilate Chuck Norris, the copy of whom becomes their leader. After a three month battle with the Sun Crusher, The Baker detonates an Original Flavor Blueberry ChozoMufin with a Light Glazing and Just a Hint of Lemon, destroying all of the X parasites. Raynor survives somehow to transfer to the real universe; this procedure is assumed to remove the X attributes from him.