Blizzard has unveiled a teaser trailer for their second installment in the Starcraft 2 franchise and this time it’s all about the Zerg.  Popular character, Kerrigan, is now a fully playable hero unit that can be directly controlled in Heart of the Swarm as players explore around 20 single-player missions.  Completing missions awards you with DNA to upgrade and unlock new mutations for your swarm.  For example, you can purchase an upgrade so when your banelings die, they split into two lesser banelings and continue to attack.  We don’t have an announced release date, but expect Starcraft 2: Heart of the Swarm in 2012. [via IGN]