Unusual
These crystals don't seem to have any real use, except for maybe as a weapon in a strange situation. They produce some pretty unusual things.
-Rainbow Smoke Crystal: This crystal produces a fascinating multi-colored smoke effect. It's normally only good for entertainment.
-Slime Crystal: These are goop producers. Never combine this with an Eruption Stone.
-Feather Crystal: This crystal gives off feathers when it explodes.
-Swarm Crystal: This crystal changes objects into a swarm of angry insects.
-Hypnosis Crystal: Though not that unusual, the Hypnosis Crystal has been placed in this category because of the success of its strange use (and the fact that it fit no where else). When properly charged, these crystals can send even the toughest mind into a deep trance and eventually to sleep.