Magical & Mystical:
* Enchanting
* Ethereal
* Legendary
* Mythical
* Magical
* Supernatural
* Otherworldly
* Spiritual
* Dreamlike
* Whimsical
Physical:
* Graceful
* Elegant
* Majestic
* Powerful
* Swift
* White
* Horned
* Spiral-horned
* Pure
* Pristine
Personality:
* Gentle
* Pure
* Wise
* Innocent
* Courageous
* Noble
* Protective
* Mysterious
* Shy
* Independent
Symbolic:
* Hopeful
* Purity
* Innocence
* Power
* Magic
* Strength
* Beauty
* Uniqueness
* Mystery
* Wonder
Metaphorical:
* Rare
* Unique
* Unattainable
* Dreamy
* Idealistic
* Unrealistic
Descriptive:
* Glittering
* Rainbow-hued
* Shimmering
* Silvery
* Sparkling
* Magical
* Glowing
* Captivating
* Enchanting
* Bewitching
Negative:
* Feared
* Misunderstood
* Endangered
* Extinct
* Dangerous
* Untamable
The best words to describe a unicorn will depend on the specific context and how you want to portray it.