Mote of Light
Source: Vendor. Q : "How do you guys determine what will become a toy?" A : "We throw back a shot of vodka and take aim at the "toy or not-toy" dartboard." (Tom Chilton) True story, from Reddit.
Mote of Light is a toy sold by the vendor Xur'ios in Dalaran during the Legion expansion, transforming your character into a transparent starry celestial figure.
Guide awaiting review
Locate Xur'ios in Dalaran
Find the vendor Xur'ios in Dalaran. He carries a variable inventory of rotating items, so Mote of Light may not always be visible in his stock — check back periodically until it appears.
Purchase Mote of Light
When Mote of Light appears in Xur'ios's inventory, purchase it for 
50 Curious Coins. The item is not consumed on use and can be activated repeatedly.
Tips
The celestial appearance pairs well with
Reins of the Astral Cloud Serpent, 
Celestial Steed, 
Fang of Oblivion, 
Starshard Edge, and 
Elegion, the Fanged Crescent for a fully celestial theme.The character model for the effect is scaled to a Human/Night Elf/Blood Elf size regardless of your character's actual race.
