Assuming you've utterly gorged yourself on icing-laden birthday goodness , TERA players are now qualified for a weirdo sort of treasure hunt that culminates in your coming into control of a gibbering, only vaguely terrifying new mount.
Gift boxes have been strewn haphazardly across Arborea, and while some may contain unspecified "other items," you'll want to be on the lookout for the letters spelling out the name of your favorite MMO. No, not Rift—I mean T-E-R-A! Once you've collected the all four letters, click on the "A" to receive the Gourmando Amount skill book, from which you can learn to ride, well, this fruit-basket-topped thing:
En Masse have created an FAQ for the event, but the most pertinent facts you'll need to know are that A. the spell book is tradeable (so if you can't be bothered, you can probably expect another player to sell you one for an extortionate price) and B. the event ends May 31. So get up and get searchin'; Gourmando's not going to stick around forever, but cake will always be there for you, even at the end of the birthday month.