Flying creatures are often the ones that can be a trouble to defeat in The Witcher 3. Unlike Ciri, Geralt can't transport anywhere he likes to. That means he has to get to their nests by foot or by other more simple means. As an experienced Witcher, Geralt also knows that an attack from above can be highly dangerous. Especially if the monster also has some other unpleasant traits, such as spitting fire or poisoning the enemies it faces.
Luckily, flying monsters aren't as common in Geralt's world as other beasts. He mostly comes across them in Skellige but they appear in all major lands of The Witcher 3 - even though there are only a few basic types.
5 Basilisk
Basilisk is a dangerous and strong creature. However, it appears only rarely in The Witcher 3. And unlike in mythology, it doesn't turn people into stone by looking at them. Like with any flying creatures, it's a good idea to use Igni against basilisks. Aard can also help, knock the basilisk out of the sky. Its most notable presence is in the quest Ciri's Story: Out of the Shadows. In the quest, Ciri races the Bloody Baron, a basilisk shows up and she uses her powers to save the Bloody Baron from the monster.
Another sighting happens in Toussaint. Geralt encounters a rare silver basilisk. He can choose to kill it or spare its life. If he spares the basilisks, its owner and protector will be very grateful to Geralt and will give him money. This happens in the quest Mutual of Beauclair's Wild Kingdom.
4 Cockatrice
Just like basilisks, cockatrice is relatively rare in The Witcher 3. And it's possibly a good thing since it's a tough beast, fast, strong, and merciless. The Aard sign helps to fight the cockatrice and Geralt can also use Grapeshot to somewhat level the playing field. Geralt can make the fight easier by attacking the cockatrice from behind. Because of its size, it takes the cockatrice a while to turn around.
The most significant cockatrice appears under the name 'shrieker' in the contract also titled Shrieker. It resides near Crow's Perch in Velen. An interesting fact is that cockatrice has its own Gwent card!
3 Forktail
A forktail looks a bit like a dragon. But dragons are incredibly rare and forktails are smaller and not as intelligent. Despite that, uneducated people can mistake the two in the game. They're poisonous so Geralt should always have the Golden Oriole ready.
Geralt will encounter a forktail multiple times in the game, most notably in Skellige where the contract's issuer believes it to be a dragon. If Geralt tells the man the truth, he will get less money, so it's better to lie and claim the forktail was indeed a dragon. This happened in the quest Dragon taking place on Fyresdal, in Skellige. Just like a cockatrice, forktail has its own Gwent card.
2 Wyvern
Wyverns are able to snatch their prey and carry it away for future use. They attack both animals and people. They're venomous which makes the fight against them challenging. Preparing a Golden Oriole before the fight is the best way how Geralt can protect himself. Geralt can try to bring them down, on the ground, by using the Aard sign against them. Wyverns appear in multiple contracts in the game, most notably in Velen when one of them finishes off an entire patrol of Nilfgaardian soldiers. This happens in the quest Patrol Gone Missing.
If the usual wyvern wasn't dangerous enough, The Witcher 3 offers an even deadlier alternative. It's the royal wyvern, a larger and aggressive beast. A royal wyvern lives near trading routes and attacks the travelers. Geralt encounters one in Velen, in the quest Phantom of the Trade Route. He can either kill the wyvern before or after he spoke to the man who issued the quest. Either way, he will get his money in both cases, even though he won't be able to save the man the royal wyvern had snatched before.
1 Slyzard
Slyzard is another flying beast that people can mistake for a dragon. It's a large and powerful creature that most notably appears in Toussaint in The Witcher 3. Slyzards are extremely dangerous because they breathe fire. The best course of action for Geralt is to deal the creature a single strike, dodge its attack, and repeat this over and over again. He can also use his crossbow against it while the slyzard is in flight.
A special quest associated with this beast is called Bovine Blues. Geralt will come across a man crushed by a cow that fell from the sky. His investigation will reveal that a young slyzard dropped the cow. It wanted to carry it into the nest but the cow was too heavy. Geralt then can track the slyzard into the nest. He kills it and will also have to deal with the slyzard matriarch, the young slyzard's even more powerful mother. Alternatively, Geralt can stumble across the nest before he ever takes on the contract and kills the slyzards in advance. He will still get paid for it later if he does.