When StarCraft players complain about balance, there's one unit that comes up often: the Mutalisk, a flying lizard alien that can be used to harass workers and destroy buildings all over the map. They're especially bad if you play Protoss.
In the latest episode of the animated series Starcrafts, the Mutalisk takes centre stage, harassing the hell out of the Protoss (and immediately dying to the Terran). Mutalisks are speedy and easy to micro-manage, so a lot of players have trouble dealing with them.
As a Terran player, this is my favourite part of the clip: