Sonic Boom is one of the 32 Playble Characters in Skylanders.
Long ago, Sonic Boom took refuge high atop a mountain peak in the far reaches of Skylands, hoping to keep her griffin hatchlings safe. But despite her precautions, a devious wizard tracked her down and placed a wicked curse on the griffin eggs. Once hatched, the young hatchlings can live for only mere moments before they magically return to their shells... only to be hatched again in an endless cycle. Wanting to prevent such evil from happening to others, Sonic Boom joined the Skylanders and has trained her young to defend Skylands each time they are hatched.
Source: The Game Website.