https://www.gamespot.com/articles/free-overwatch-kerrigan-skin-is-out-now-for-starcr/1100-6457197/

Overwatch's tribute to StarCraft is now available. A free Kerrigan skin for Widowmaker can be yours by simply logging into the game anytime between now and April 3. The skin gives Widowmaker a Terran makeover, outfitting her with the look of StarCraft's most famous Ghost–at least, before she became the Queen of Blades.

This is one of several cross-promotional goodies Blizzard has planned to celebrate StarCraft's 20th anniversary on March 31. Starting today you can also get portraits and decals by logging into StarCraft: Remastered and StarCraft 2, and a Battlecruiser pet in Diablo 3. Hearthstone will get a StarCraft-themed Tavern Brawl on March 21, Heroes of the Storm will sport anniversary portraits starting on March 27, and World of Warcraft will get its own StarCraft pets.