In The Witcher 3: Wild Hunt, bestiary is among the most useful instruments because it gives you an idea of how to fight against and beat monsters. Anyway, it could be not enough to help you win those combats so, apart from knowing well who or what are you facing, it is important to learn the basis in terms of weapons and skills.
Let's take a look at how to do to beat a good amount of The Witcher 3: Wild Hunt monsters, then, remembering this short lesson.
Weapon: Silver
Bombs: N/A
Oils: Cursed Oil
Potions: Thunderbolt
Signs: Quen
The Strategy: With werewolves, you have to be very aggressive.
1) If you anticipate fighting a werewolf, prime Geralt with a quick quen and coat your blade in cursed oil.
2) As soon as you spot the werewolf, start to watch for him to start sprinting around.
3) When he approaches, quickly dodge to the side and immediately go on the offensive.
4) Down a thunderbolt, and chain three strong attacks.
5) After the third attack, dodge away from the werewolf.
6) Repeat from step 3. Obviously, you don't have to continuously take thunderbolt potions; just take them when they run out.
Weapon: Silver
Bombs: N/A
Oils: Necrophage Oil
Potions: Tawny Owl
Signs: Quen, Igni
The Strategy: Foglets are bloody annoying. These turds will almost always be invisible, and will generally spawn a fog buddy to throw attacks at you. If at all possible, try to only fight one foglet at a time, or you may get rather confused and anxious.
1) As standard procedure, if you plan on fighting a number of foglets, prime with quen and necrophage oil.
2) When you see the foglet, close distance fast
3) If the foglet takes the bait, it should disappear into mist and you might notice a transparent version of it flicker briefly. This is the fog buddy I mentioned earlier.
4) As soon as you see the fog buddy, use igni to kill it.
5) Go on the defensive and watch the original foglet's cloud. It will likely be moving in circles for a bit, and will eventually start to move towards you. Wait until it's within striking range, dodge to the side and begin throwing out strong attacks. If you timed it right, you should catch the foglet right after it's initial attack and start to stunlock him.
6) Keep up the assault for the standard three swings and then roll out.
7) Repeat from step 3. You may have to fight foglets by ear a bit more than the previous monster, but this is roughly what you can expect to easily take care of a foglet. Minor spoiler alert: I used this technique to flawless the boss foglet at the end of a certain level 12 witcher contract.
Weapon: Silver
Bombs: N/A
Oils: Wraith Oil
Potions: Tawny Owl
Signs: Quen, Yrden
The Strategy: These didn't particularly give me too much of a trouble, but I figured I should add another monster to this list before people start calling the guide dead.
1) Prime with quen and wraith oil.
2) Slap down a yrden trap and kite the wraith into the trap.
3) Immediately begin spamming fast attacks until the wraith has been pushed out of the circle.
4) Roll away, reapply quen, and repeat from step 2. Wraiths are fairly simple monsters to fight, but as I said, I figured I'd leave what I've been doing to flawless these guys.
Weapon: Silver
Bombs: Dragon's Dream (Fiends, Griffins)
Oils: Relict Oil, Hybrid Oil, Draconid Oil
Potions: Blizzard, Thunderbolt
Signs: Quen, Igni
The Strategy: Fiends, Griffins, and all Draconids are intimidating, and not just because of their size; they're rather unpredictable and can occasionally throw out a debilitating attack at breakneck speeds. It's because of this that I recommend keeping a blizzard potion at the ready (particularly for fiends), along with a thunderbolt so that you can fight them in short, close-quarters bursts.
1) Coat your blade in relict, hybrid, or draconid oil and cast quen on yourself. I wouldn't bother trying to use alternate quen to heal in this fight; they will usually break it on the first hit and deal damage instead.
2) Keep your distance at first and, like with the werewolves, watch for them to do a charge attack. Obviously, move out of its way.
3) Muster together your courage, pop the thunderbolt first and follow with a blizzard a couple of seconds after. As soon as the thunderbolt takes effect, close distance and start circling around them using dodges and fast attacks. If you time this right, you should get one or two fast attacks in before the fiends can recover from the charge, and by this time you should have a blizzard active so that you can time your dodges to move out of the way of its attacks.
4) When your thunderbolt runs out or you get hit, dodge out of his range and use igni. The point here isn't just to do damage but rather to stun him, so use the alternative mode if you have it; alternative igni has essentially a 100% chance to stun monsters that are without ignition immunity.
5) Repeat from step 3. Fiends are similar in approach to wyverns, griffins, etc in that most of their attacks are more akin to burst damage; they may take a while to wind up, but they do so typically subtly and the attack itself is generally fast and hard hitting.
Weapon: Silver
Bombs: Moon Dust
Oils: Vampire Oil
Potions: Tawny Owl
Signs: Quen, Igni
The Strategy: I don't really know why I'm actually putting this here, 'cause all vampires are practically jokes to fight. You could kill these with igni alone, to be honest.
1) I guess you could prime with vampire oil and quen, but it's really not needed.
2) Sprinkle a dollop of moon dust on the vampire when you see it and then chug a tawny owl.
3) Kill it with fire. Close the distance and immediately begin using alternate igni. Because vampires are weak to fire (ridiculously so), they take insane amounts of damage from it, and will be stunned for the next couple of hours. By the time they recover from the ignition stun, your stamina should already be back (tawny owl), and you can burn it some more. Too easy.