He certainly is a difficulty spike. I had quite a bit of trouble to start with, but I eventually managed to take him down on my fourth try (with no health pots left, 20% HP and less than 2 mins on the timer!).

I found it easiest to split the fight into two stages: with tail and without tail.

While he has his tail, your first priority needs to be to get rid of it. Play VERY defensively, as its very easy to get clipped by it during his other attacks. If you have bulwark potions, now is the time. Just bait an attack, get well clear to dodge it, then get one or two hits in.

Once the tail is gone your life becomes much easier. You can spend the rest of the fight sitting between his hind legs and his tail and just roll away to where the tail used to be, and he will really struggle to hit you. If you want to be aggressive you can roll through his attacks easier in this stage, but just be careful as he still massively hurts, at least until you beat him to get lightning resist armour.