This dashing Pegasus pony exists solely in the tubes of the interweb. He is rarely seen directly, but his presence is naturally recorded - as is the way of the interweb.
One can follow Mattatatta's day-to-day musings and activities by monitoring his favourite places to share information: FimFiction, deviantArt, and Tumblr. This digital entity has also been known to leave comments on EqD and Derpibooru, the latter of which he seemingly never leaves except to go home and sleep.
Mattatatta's residence in the vast world of the interweb is unknown, though it is theorised he has a hay pile in his metaphoric apartment in Tumblr. He often shares in Tumblr that that he frequently "hits the hay" at the early hours of the morning. It is unknown if this is actually a euphemism for something much more questionable or not.
Somewhere in his rapid, but limited scope of movements across the tubes, Mattatatta finds the time to write pony fanfiction, create pony fanart, and play a variety of games. If you see a Mattatatta on Team Fortress 2, he is most definitely not a spy. Unless it really is Mattatatta playing as a Spy, which is different.
Overall, Mattatatta is considered to be an introverted entity, living in an extroverted world. Without a Cutie Mark of his own, nopony knows what Mattatatta's true destiny is, but the pony doesn't mind. When the world he lives in cares more for his simple mug shot than a picture of his posterior, when his variety of minor talents bring him enough simple pleasures to sustain himself; this pony can afford to try anything his heart desires, and wait for his mark to finally appear.