In Starcraft 2, the mortal enemy of the Zerg race. Captain Phoenix will kill your queens, kill all your overlords and supply block you, kill mutalisks in 1:2 ratios, lift up and slaughter most of your ground units, and just generally make your life hell. Not as dangerous in 1v1 where he can safely be counter attacked or defended against. In team matches however, particularly 3v3 and 4v4, if Captain Phoenix is left alone to get a critical mass of phoenix your team is in a large amount of trouble if you don't have a Terran player. At the very least, Captain Phoenix will shut down almost all production from enemy zerg players.
The protoss on the enemy team is walled in with a core and gate at the ramp, so is the protoss on your team. The toss on your team is going stalkers, and there is a good chance the opposing protoss is also, but little do you know you're up against Captain fucking Phoenix. If you went ground, you have already lost, you will have little to no defense vs Captain Phoenix. If you attack, your forces will be lifted up and killed, with the exception of mass zerglings, which will just die at the ramp. By now most of your overlords you spread out will be dead, if you are supply blocked it's probably also game over. If you went air instead of ground, you're DEFINITELY dead. Mutalisks will be slaughtered by phoenix kiting, and while corruptors may be able to go toe to toe with phoenix, they are completely useless against anything else the protoss will send aside from assisting with corruption.