It's unusual that a character in a new video game makes her debut in another one first, but such is Blizzard's freelancing approach to Heroes of the Storm, where Tracer of Overwatch will show up before that game's full launch next Month.
That means that for most, the introduction to Tracer and her abilities will be in a MOBA, not a first-person shooter. For Heroes of the Storm, she is "an extremely mobile ranged assassin," thanks to her time-warping "blink" ability that is canonically explained in this video's introduction. The inverse of that is "recall," which not only is an evasive move backward, it clears her of most debuffs.
Her attacks are standard fare: twin pistols and a melee. Both charge up her only heroic option: the pulse bomb, which is upgradeable. The video above has much more detail.
Tracer is being offered as a preorder incentive for the Overwatch: Origins Edition on Windows PC; anyone buying a copy of that will get her in Heroes of the Storm on April 19. The rest will be able to buy Tracer in the Nexus beginning April 26.
Overwatch itself launches on May 24 on Playstation 4, Windows PC and Xbox One. Anyone who preorders the game will get early access to an open beta (all platforms) from May 3-4, with everyone else getting a crack at it from May 5-9.