A Test Of Will
A Test Of Will is the fourth and final quest at the Exploratorium. It is accepted immediately upon accepting the previous quest, Timber! His Arms Wide! It requires the player to find a way to Mushroom Island and defeat the Mind Blight.
The entrance to Mushroom Island is immediately south of the Overgrowth South Warpstone. The entrance is blocked by red flowers. If you recall the dialogue from the Sapling Sampling quest, you may remember that red flowers only open at night. There is a convenient campfire here that will allow you to rest until evening so you can enter the Forgotten Passage
At the other side of the Forgotten Passage, you find yourself on Mushroom Island, and you must now traverse the island to find The Anomaly.
The Anomaly is a two level dungeon featuring Succubus, Naga, Phantom, and Gazer enemies.
At the end of the dungeon, you fight the Mind Blight. While it can be defeated with just plain DPS, it will take quite some time. Periodically, the Mind Blight disappears and three mirrors appear in front of you and pulse in a particular order.
If you attack the mirrors in the order indicated, it deals a heavy blow to the Mind Blight. After just 4 of these cycles, you will have defeated the Mind Blight and the quest will be complete. If you hit them in the wrong order, Phantoms spawn and the cycle continues.
Once the Mind Blight is defeated, you appear back in front of Mother in the Overgrowth. After talking to her, the Quest is complete.