From Destinypedia, the Destiny wiki
Very little is known of Starhorse, however it has been seen to be capable of summoning seemingly anything and anyone from across the paraverse — realities different from our own — to participate in Dares of Eternity, a game show of its own design. Along with this, it has been seen to also be capable of speaking directly into the mind of those it wishes to, however without Xûr, Agent of the Nine to translate its words, they come across as a variety of brays and neighs, exhibiting different emotions and intensity. Starhorse has been seen capable of manipulating ability-enhancing energy; from instantly recharging grenades and melee skills, to being able to supercharge Guardian's Super recharge time and mobility. Starhorse has also been seen capable of bestowing a buff known as Starhorse's Favor which provides the granted regenerating heavy ammo and a bonus to personal defense.
How Starhorse is capable of performing all this is unknown.
Personality and traits
Not much is known about Starhorse. They appear to create things for their own entertainment, such as Dares of Eternity. They also appear to be comedic.
List of appearances