Alien Swarm Parasite

The Alien Swarm Parasite is an unlockable headwear item for all Classes. It is obtained by earning the Hat Trick Achievement in the game Alien Swarm.

Trivia

Hat Trick Achievement Icon

• The Hat Trick achievement is earned by completing 2 co-op missions online.
• This is the second hat that appears to be a still-living creature, the other being the Triboniophorus Tyrannus.
• The Parasite's tail has jiggle-bones making it the second promotional hat with jiggle-bones, the other being Max's Severed Head.
• This hat is the first and only item to be unlocked via the achievements of another game.

• This hat was speculated days before the game was even released. The achievement icons were seen before hand and people noticed that the achievement icon's character resembled the Heavy.