Gargoyle
A gargoyle is a winged variant of the termagant and possesses the same armament, except for a venom gland that allows it to spit acid. While being weak and cowardly, shying away from combat without a synapse link to nurture it, gargoyles are described in the fluff as being lethal in a confined space, with claws, spikes, tails and flapping wings and venom flying everywhere. They typically like to dive bomb exposed and weakened units like Guardsmen command squads, as they are not able to defend from a swarm of giant, acid spiting, gun toting bats that flock you like your simply the most tasty piece of icing on a cake and flying off again. They love units like command squads, artillery commanders, heavy weapon teams and even snipers. Anything alone and unable to fight back at mid and close range a labelled "dumplings" to them.
On the Tabletop
Termagaunts with wings and a hefty points increase. Rather unpopular, but not any more so than the rest of the Tyranids 5th ed. Fast Attack choices. You need to know what you're doing to get the mileage out of these guys.
In game they have one to two uses. Use one is to have them Deep Strike right behind enemy lines, away from fighting, and then attack things like command units, snipers, heavy weapon teams, gun emplacements. They will wipe out these things through fleshborer fire, (takes around 20 to start working) and if the unit is down to two models or one wound, dive in and use their acid to finish them of.
The second use is to take a unit of 30, then have it deep strike right next to your flying hive tyrant. Then your tyrant can have cover, as well as another 30 attacks to aid him. A smashing combo uses two winged hive tyrants with twin linked devourers, and 30 gargoyles each, to rape the living shit out of enemy lines. Place them where the enemy has a crap load of immobile artillery and vechiles with weak-to-moderate rear armour and then pelt them to death with so many dice rolls they drown in them, and it takes a whole new agency of the administratium to process the results. Works well against Tau and Imperial guard.
Really though, gargoyles are simply bats with guns, and use numbers (like all Tyranid's) mixed with speed, to force an opponents death from aforementioned dice drowning. Dakka on wings. Gargoyle models also are now plastic,not the hellish metal ones. Gargoyles would be better if they could use devourers. But then flying dakka bats with acid spit would be absurd. Unless Matt Ward wrote it. Update: Dakka spit bats have now been done: See the Hive Crone for the shining example of loldom.