Mysterious Portal

The Mysterious Portal instantly opens at the start of the Old One's Army event. The Mysterious Portal cannot be destroyed, and two of these will spawn 235 tiles on either side of the Eternia Crystal Stand. They are responsible for all the enemies that spawn in the event, and they despawn upon the event's completion or failure. When standing in the portal while a wave is currently happening, you will continuously take damage.

Tips

 * A good way to keep the enemies at bay near the Mysterious Portal is by placing an Explosive Trap near the portal's entrance. This way the enemies will instantly take damage when they come out.