Wait till u get to the draug, it makes the kayran look like a worm.
Here is how i beat the kayran on dark: died 3 times.
1.DISABLE THE GODDAM $@*^*$^@*^o( QTE urghghghgh i hate it
2. Roll like a goddam maniac. Always look into the sky and see when the tentacles are gonna hit and where.
3. POTIONS! You must have 'Swallow' up and running in this. It heals the vitality if you got hit. I also recommend completing Metiele's heart to get the extra +1 regen. I m running on alchemy tree and i have Swallow, tawny owl(regens vigor i think) and rook. Dont bother getting the ostmurk/mongoose thing. Just go with Sile to the boss.
4. I recommend getting the kayran trap. But sometimes the monster wont get caught by the trap for unknown reasons. Just gotta reload. I recommend the 2nd tentacle to be trapped like this.
5. At the kayran you should have at least 3 vigor boxes. Always save 1 for Quen!!!! It is a life saver. Here is what i always do: Quen first, then Yrden, then if i didnt get hit, i save the last box and run around like mad. Then when it is time to hit the 2nd tentacle, my Quen should have expired and i should have at least 2 vigor bars. Rinse and Repeat.
6. I recommend going for the front 2 tentacles first, then go for the left tentacle. Dont go for the extreme right one cuz that one seems impossible to cut. If u die, reload reload.
7. Also, i recommend you to get the Hunter's armor, and witcher's superb Silver sword. At dark level, armor rating doesnt seem to matter as u will get one hit by the kayran anyway. On normal it does matter. Use the silver sword's powerful swing button to destroy the tentacles asap. If not, the yrden wears off and u wasted 1 chance.
8. If u r lagging then turn down everything to low. Once the kayran is down by the stone tower thingy, just roll like mad towards the kayran. It should be easy at this point.
9. Always..always have quen up. Always roll.
10. Dont join the imperials or befriend solitude guard