RadP: Can you write me here anybody some detailed tactics how to kill Kayran? I tried several times but I am killed in a while every time. I really don't konow how to play this fight. This is the reason I stopped to play this game. Is killing Kayran necessity in proceeding with this game further? Please help me.
First, did you make the potion that Triss asks you to make, using the ostmurk? If not, you should mix it and drink it before the fight. It will make you immune to the Kayran's poison.
If you have the Kayran trap, place it and then wait near it. When the Kayran lifts its tentacle, dodge out of the way, and the tentacle will get stuck in the trap and get cut off.
If you don't have the Kayran trap, use your Yrden sign to place a magical trap on the ground. Then do the same thing, waiting for the tentacle to raise up, then dodge to one side as it comes crashing down. It will get stuck in the Yrden trap. Then run up to the big, glowing red part of the tentacle and attack it. Geralt will cut off the tentacle.
Repeat this a few more times. If you used the trap, you'll have to use Yrden on the next few tentacles. Occasionally the Kayran will sweep its tentacle sideways, which can be a little hard to dodge. Sometimes it also gets mad and attacks with several tentacles at once, which you just need to dodge.
Eventually, after cutting off enough tentacles, you will trigger the QTE, where Geralt will ride on the Kayran's tentacle for a while. I recommend turning off "difficult QTEs" in the game menu, to make this section less annoying. After this, Geralt needs to climb the broken bridge to get at the Kayran's head. It will throw rocks at you. Use the Quen sign to avoid damage from the rocks, or you can try and take cover behind the rubble. When you get to the top, Geralt will automatically finish off the Kayran in a cutscene.
Don't forget to loot the Kayran's corpse, as it has several unique ingredients for crafting.