When the Chaos statue goes down to half health, Medusa will come out and petrify all of the player's units except those in the player's garrison and those just outside the enemy's garrison. The enemy statue will stay invincible until Queen Medusa is killed. When Queen Medusa is attacked by units, she will use Petrify to kill the nearest units and when they get to her she will spam Venom Flux. Once Queen Medusa is killed, the enemy statue will lose all its health after a few seconds and the player will win the game. If Medusa is not killed, she will Petrify the player's statue until it crumbles, and then the player will lose the game.
When Medusa petrifies everyone (except the units in the locations described above), she seems to say something like "You all must die!!"
When Medusa spams Venom Flux, she says something like "Toxica massicus!"