The Mezada is the creation of John Carr and is his online persona.
Every card in the every graveyard is revived, creating a mass resurrection for all but the Mezada and his opponent.
Mezada has a very useful ability if this card is destroyed. It causes all units in all player's graveyards to be revived and placed in their hands. This can be a particularly devastating move on the final turns, allowing you to play some units lost to the graveyard. If you are able to place these units in your villages, you'll gain some much needed points. In particular, animals would be the most useful, especially the Pig for that final attack.