Even though Geralt has plenty of different things to do in The Witcher 3, most of his time is spent fighting various monsters, as well as humans who stand in his way. Geralt has to take on some of the enemies while he searches for Ciri. There's also the battle against the Wild Hunt which puts formidable villains in Geralt's way.
And if that wasn't enough, the witcher's job is to kill dangerous monsters who hurt or kill people. Geralt can take on a rich variety of contracts in the game, and he faces multiple bosses, but some of them are simply more challenging than others.
10 Royal Griffin
The royal griffin makes it onto this list since he's the first boss Geralt faces in The Witcher 3 - which can make fighting him difficult for new gamers who haven't been playing the game for long by this point. Geralt has a rich variety of options how to fight the royal griffin - he can use his crossbow, sword, or a bomb, if he has any at his disposal. But one strike from the griffin can cause a lot of damage, so if Geralt wants to defeat the beast, dodging is the key.
9 Nithral
Nithral isn't such a powerful boss, at least in comparison with others. He still deserves a spot on this list, however, since he's the first Wild Hunt warrior whom Geralt fights - on a relatively low level. Geralt meets Nithral when he's searching the Elven ruins alongside Keira Metz. Nithral is strong but not very fast. Several times throughout the fight, he creates a shield around him and regenerates. He also sends Wild Hunt's hounds against Geralt - but with a clever maneuvering, Geralt can kill Nithral in the end.
8 Eredin
Eredin is the final boss of the base game, the leader of the Wild Hunt who pursues Ciri and wants to use her powers. Eredin is a strong fighter and he possesses magic, which gives him an edge over Geralt. But he's not the strongest enemy in The Witcher 3. As long as Geralt stays out of reach and dodges Eredin's magical attacks, he should be able to finish him off relatively fast.
7 Crones
Crones are one of the most dangerous creatures of The Witcher 3. They eat children, curse people, can kill the baron's wife Anna, and they also try to eat Ciri. Geralt and Ciri later go to the Bald Mountain and Ciri fights the three witches alone.
The fight is challenging since Ciri isn't as strong as Geralt and she faces three opponents, not just one. However, with clever usage of her skills, Ciri can eventually cut the Crones down (even though one of them always survives).
6 The Shaelmaar
Geralt fights the shaelmaar moments before he meets Anna Henrietta after his arrival in Toussaint. The shaelmaar is a new type of monster which means the player has to figure out how to fight it - and before they do, they can die a few times. The shaelmaar is fast and it tends to roll around. If it knocks Geralt down and rolls over him, it does a lot of damage. Geralt should try to strike it when it's not rolling around like a ball and uncovers its belly, that's when the shaelmaar is at its most vulnerable.
5 Imlerith
Fighting Imlerith is, funnily enough, more challenging than taking on Eredir. Imlerith is one of the generals of the Wild Hunt and he's the one who kills Vesemir. Ciri then decides to get revenge and asks Geralt to help her. They go to the Bald Mountain and Geralt faces Imlerith. The fight can be quite long since Imlerith uses his giant shield and it's difficult to get past it. The best chance is to try and get behind Imlerith. Once he loses a portion of his health, he drops the shield, and that's when the fight becomes easier. He can also teleport around the battleground, so Geralt should be wary of where Imlerith will appear next.
4 The Caretaker
The Caretaker, whom Geralt meets at the Von Everec estate, is by far one of the most frightening creatures of the game. He's quite slow but very strong and each hit the Caretaker deals Geralt causes a lot of damage. Geralt should protect himself by using Quen and dodging.
The Caretaker also summons dark spirits during the fight which will attack Geralt and make the combat more difficult. Geralt should try to defeat the spirits as fast as possible or he'll risk the Caretaker healing, and Geralt will then be right where he started.
3 The Bruxa Of Corvo Bianco
Geralt takes on vampires multiple times throughout the game - but the bruxa at Corvo Bianco is the first bruxa he ever fights. That can make it difficult to defeat her at first since the player doesn't know what to expect from the vampire. She moves very fast, can become invisible, her sonic wave throws Geralt back and makes his ears ring - and, of course, she'll try to drink Geralt's blood. Geralt should drink Black Blood before the fight and use the Vampire Oil as well as the Moon Dust bomb to stop the bruxa from turning invisible.
2 The Toad Prince
The Toad Prince is a giant monster living in the Oxenfurt sewers. The toad doesn't move around much but it uses its venom against Geralt which slows him down every time it hits him. The Toad Prince also jumps and when it lands back on the ground, the impact can hurt Geralt. Geralt can use several extras against the monster - such as the Northern Wind bomb or the Cursed oil, but in the end, the fight is all about staying patient and keeping Geralt's health up with food and potions.
1 Dettlaff
Even his fight with the Corvo Bianco bruxa and various other vampires can't prepare Geralt for his match against Dettlaff. Dettlaff is the most challenging boss in The Witcher 3 - since Geralt can't actually kill him, and Regis has to finish Dettlaff for him. The fight has several stages, and a single strike from Dettlaff can severely bring down Geralt's health. There's a way to avoid it, but in order to do that, Syanna has to die and Geralt has to allow Dettlaff to walk free - otherwise, they will end up fighting to the death.