The Jewel of Light is a Master Mode-exclusive light pet-summoning item that has a 25*1/4 (25%) chance to be dropped by the Empress of Light. When used, it will summon a pet Fairy Princess that provides pink-colored light. It is fast and will always position itself slightly elevated behind the player.
Despite being exclusive to Master Mode, the fairy does not possess any unique abilities, such as the Wisp in a Bottle's manual repositioning or the Suspicious Looking Tentacle's treasure sensing. This, combined with the fact that it still has the same brightness as those items (120%) might render its usefulness rather limited.
However, one might prefer the fairy for its lighting color and static positioning behind the player's back.
The pet that is summoned is very similar to that summoned by Frozen Crown, and has the same flight patterns.