The Ghost Hydra is a legend of the military plane Hydra that can be seen flying during stormy weather on Mondays only. The Hydra appears to be damaged, as you can just make out black smoke coming from both its wings. Players speculate that this plane is maybe mistaken for another type of plane that commonly fly through the sky, but on closer inspection it appeared to be a Hydra. Most people guess that the game codes just spawn the wrong plane. The "Ghost Hydra" easily out-speeds the player when he attempts to follow in another plane.
The only place the Ghost Hydra has been spotted is above the city of San Fierro, during stormy weathers on Monday.