Sarah Kerrigan's unit underwent numerous changes during the development of StarCraft II: Heart of the Swarm. Kerrigan could also increase her health, damage, armor and energy through upgrades unlocked by completing bonus objectives. By May 2011, Kerrigan had four skill sets, although not all had been developed as of then. Other potential skill sets revolved around defenses, comboing with air units, stealth and "roach-burrow supporting Kerrigan". At some point Kerrigan's game unit appearance evolved as she progressed through the campaign.