A hydra is an account that is controlled by multiple players. "Hydra" can also be a verb, equivalent to "doubleheading" or "multiheading" although those terms are now obselete. It is customary to reveal to other players that you are a hydra if asked; the mod and List Mod are required to be informed who is in the hydra upon request. Some moderators also disallow hydra, or allow other players to place limits on hydra in the game (either in number, or whether any at all may enter the game).
- The first hydra anywhere might be L'layne on the Grey Labyrinth. They played as early as 2005, although the term "hydra" wasn't used.
- Two-Headed Mafia took place in 2006, with linked pairs of players each posting under their own name in the game thread.
- The first hydra to play in a regular game on Mafiascum was Gaspar (Glork/Primate) in 2007, in Dantes in Fresno.
- Xdaamno suggested a 'Hydra Mafia' in scumchat sometime prior to December 2007.
- Adel finally ran an all-hydra game (two of them, actually) in 2009.
- In 2007 BrianMcQueso put forward the idea of a 'Team Mafia' where two or more players would collaborate under each account in the game. Note that this has no relation to the later Team Mafia in-vitationals, and it involved every account in the game being a hydra.
- Yosarian2 and Xdaamno doubleheaded a Borg role for a Marathon Game in March 2008.
- xyzzy's Mini 620 appears to have been the first regular forum game with multiple Hydra involved.
- It stirred up some controversy at the time over whether or not the component players should be outed, as well as how intra-hydra communication should take place.
- In addition, that Mafia Discussion thread led to the naming convention largely switching from multi-head to hydra.
- In late 2013, discussion sprung up as to whether hydras can be considered normal, which lead to a public poll in January 2014.
- On August 12th 2014, hydras became officially banned from normal games.