Instructions
Climb to the middle floor of the fourth tower in the Ashlands. The room contains a group of Phantom Guards and a barrier preventing you from going farther into the room.
Kill all of the Phantom Guards. The barrier disappears once the last one dies. You can access a bomb flower and a Chronosphere.
Press "B" to interact with the Chronosphere. This activates the Chronomancer ability, slowing down time briefly.
Press "B" to pick a bomb from the bomb flower near the Chronosphere.
Jump out of the tower back to the ground.
Run into the bottom floor where the red crystals are located.
Press "B" to throw the bomb onto the red crystals. The bomb destroys the crystals when it explodes after a few seconds.