The tower defense is all about defending the Core. All players can attack the monsters as they invade and move toward the core. If a monster reaches the core, it loses life. When the core is destroyed, the event ends and the players lose; otherwise, they win!
In Tower Defense you can earn the new set Moist, which is obtainable via a roulette at the entrance by using Crystal Tokens. For each Tower Defense win, players receive 5 Crystal Tokens – and 15 tokens are required to use the roulette.