Blood Moon

The Blood Moon is an event that has a small chance (1/8) of happening every night. It is heralded by the message "The Blood Moon is rising...".

"You can tell a Blood Moon is out when the sky turns red. There is something about it that causes monsters to swarm." &mdash;  The Guide 

During a Blood Moon the spawn rate of monsters increases and Zombies gain the ability to open doors after attacking them several times. This can put the player's home and NPCs in peril, if they are not guarded appropriately. Monsters will also spawn inside cities, despite the natural spawn protection they give.

The benefits of a Blood Moon for more experienced players are the increased money and items they can harvest from the swarming Zombies and Demon Eyes, however it is advised that less experienced players should stay somewhere out of the reach of monsters during the event.

One way to survive a Blood Moon completely unharmed is to barricade all Wooden Doors by placing blocks beside them, as seen in the images below. A simpler way is to place all doors at least two tiles above ground, or dig a 2x2 trench in front of the door; zombies will jump to reach the door, and cannot attack the door while jumping.