psychopigeon: YOU HEARD ME ITS IMPOSSIBLE
I had to use a online video walthrough myself after 3+ hours of failure!
And that was on easy mode so your not alone Psy, its a terribly designed encounter with no forshadowing of what needs to happen!
So below is a walk through (SPOILER ALERT) for you!
Before combat drink the mongoose potion (I like to add Swallow And Tawny Cat as well)
In combat
Focus on the far left 2 tenticales, they rather easy to trap unlike the center ones (which can be caught but with much aggrevation)
Once you destroyed the far left ones, goto far right and kill 3rd tenticale
(Please note, after destroying a tenticale run to the back end of wall and stand there, Kayran cant reach you while it thrashs about)
when the 3rd tenticale is done and youve taken the ride on a remaining tentical it will smash the bridge
Once that has happened, run to far left side bhind the rumble and up the stone bridge portion
Then all you need to do is reach the Kayran and Geralt will pull out a miraculas bomb you dont have in inventory and blow up the Kayran finishing the encounter.
Actually very easy once you see it done and understand the encounter!
THIS IS A PATERN/REFLEXE ENCOUNTER, like all combat in this game, dont over think it (hell dont think at all) just follow the patern, dodge the incoming stuff best you can, and you will win!
Hope this helps you out, I was sooooo fustrated with this encounter I almost quit game entirely.
And dont feel bad you didnt figure it out, most didnt either (regardless what they might claim). It wasnt presented very well at all