As a Witcher your entire purpose is supernatural pest control, so some Witcher 3 monster killing tips will help the process progress a little more smoothly. There are notices boards to check, people to interview, and clues to chase up. A lead could come from anywhere as you explore and reading up on things like Gryphon or Noonwraith in your spare time isn't going to help adding to your bestiary. The more you know, the more weakness you can exploit, or tools you to enhance your chances.
Find a paying customer
The first step in getting paid to kill things is finding a person willing to pay you to kill things. When you walk into a town, you can go door to door searching for townsfolk with monster problems, or simply find a job posted on the town's notice board. Once you find your potential customer, it's time to meet them in person.
Mind you, the person asking for help isn't your basic questgiver offering gold and a new item for completing a task. These people have real motivations behind wanting a creature killed. Maybe this thing ate a family member and they want revenge, or the monster could be blocking a family's only source of water. Whatever the case may be, sometimes you can haggle for bigger rewards, depending how desperate they are. But be careful. Push too hard and they won't work with you at all.
Investigate the area or the locals in peril
Once you have your agreed-upon reward lined up, it's time to start the investigation. Yes, an investigation. Many times your client doesn't know the exact location of the beast or even what it is. They just know that "there's something scary out there." So, as a brave witcher, you need to find out the nature of your quarry, and you'll find many of your first clues from the local populace.
The world is filled with people, and people see things. Eyewitness accounts are your best bet in finding out what you're dealing with. In the case of my hunt for a gryphon, I spoke with a hunter who discovered a group of soldiers the creature had thoroughly gnarled on. He led me to the spot of the beast's bloody feast, which enabled me to continue my search.
Set up a crime scene, Batman-style
Okay, we know there's a gryphon out there, but what type of gryphon is it? Is it male or female? Are there more than one? Why is it killing people now when it was perfectly peaceful before? Each hunt presents lots of different questions, and discovering the answers creates an interesting side story. Some of these answers can be found in the Wild Hunt's version of a crime scene. That squad of soldiers I mentioned earlier? Their brutal deaths left a bunch of clues behind.
Using your witcher senses to scan the area will reveal the events of the attack, trails to follow, and possible monster weaknesses. In the case of the gryphon, I followed the beast's tracks to for find out what it'd been doing before the attack, only to find a dead female gryphon, and a really big, burned down nest. Turns out there's a Royal Wing gryphon on the loose that's royally pissed about people killing his girlfriend and burning his house. Right, now we know exactly what we're fighting. Time to hit the books.
Do your research
Yes, you're going to have to read in The Witcher 3. There are no tooltips, or compass markers showing you exactly where to get item A to use to kill a monster. You have to figure that out on your own by reading the bestiary. Sometimes Geralt will know the details of well known monsters off the top of his head, adding a bestiary entry into the menus for you to read and get acquainted with. Other times you need to seek outside help.
Books are useful items in The Witcher 3, but you may have to save up to afford them. Local merchants will sell books detailing the monster in question or occasionally, townsfolk will be able to give you a few details that will help you bring down the beast. Think of research as piecing together a boss guide. The books tell you what type of sword oil to rub on your weapons, what bombs the creature is weak against, and what potions will protect you from its abilities. But they also tell you how you should fight your prey. For example, fighting a noonwraith requires you to place a Yrden sign to force it into a physical form and toss a special bomb to stun it, then you're free to slash it with your wraith-oiled silver sword. Try the battle any other way and you're going to have some trouble.
Get every little detail possible
Finding the weaknesses of a monster will often set you on a search for specific bomb and potion recipes, and getting all those details correct will definitely help you kill the beast. But then there are cases in which the creature can't be killed, like say, when you're hunting a noonwraith (because it's already dead). What do you do then?
These quest-specific situations bring additional branches to the questline. In the case of the noonwraith, I had to find an item that the ghost was attached to - a necklace a murdered woman wore at the time of her brutal death and the reason why she decided to hang out in spirit form. This involved searching an old, abandoned town, jumping down a well, and recovering a rotten corpse. Not the most glamorous of jobs, but at least the wraith won't return when I lay her necklace and body to rest (after I kick her ass).
We're almost there. It's nearly time for the final confrontation. But before you jump into the deep end and bring silver sword to flesh, bone, or ectoplasm, there are preparations to be made. Everything comes into play when you're facing a dangerous beast. Before a fight, witchers drink potions to increase their strength and build immunities. I mean, it would make things easier if you were unaffected by the poison a monster spits in your face, right? Potions let you do that.
Once you have your bombs lined up, potions gulped, and swords oiled, there are even more options to use. Traps can give you a huge advantage in battle. You just need to set them up before you summon your prey and the fight begins. Even the time of day can play into a battle. Noonwraiths are called noonwraiths for a reason. They are strongest around lunch time, so it's better to face them at night. Once again, it pays to read that bestiary.
Kill the damn thing
All of our time and effort culminate in this one battle. You've read about its weaknesses, you have the tools to exploit them, and you and Geralt are jacked up Mountain Dew and potions, respectively. Place your lures and the battle is on. Be careful though. You might have the knowledge, but you still need the skills to win the fight.
Even with all of the advantages of the bestiary and preparation, each monster battle is still a challenge. It doesn't take many slashes from a gryphon claw to gut a witcher. Time your attacks carefully, use your sign magic, and don't forget about your traps, and you just might survive.
Collect your trophy and gratitude
You killed it! Time to reap the rewards of your long and arduous hunt. Not only do you get a hefty payout for ridding a town of a menace, witchers know how to chop up monsters and make use of their helpful bits. First you get trophies, which make nice decorations and give you a stats boost, then there's all those extra entrails you can use in armor crafting and potions. Mmmm. Delish.