This strange boss might prove difficult for some players. Though only attacking while aggravated, this optional bearded giant will leap on you the moment you enter the room. The strategy or ‘deal’ with him, like with some other smouldering Dark Souls 2 bosses, is rolling around him and avoiding his attacks.
If your attacks are timed correctly, you can strike him and kill him with ease. But of course, fast reflexes are always at play when it comes to such opportunities.
Vendrick is a one-hand wielding giant who uses right hand attacks, so your best bet would be staying at his right side. The key of avoiding his attacks is rolling the same way his swipe attack occurs. So, if he’s attacking in swipe motion from his right hand to the left, roll to his right. If he swipes from his right hand to the right, roll to his left.
Follow and anticipate Vendrick attacks with attention, because he, most of the time, will try to trick you; starting to sweep to the left, when he suddenly, he will change direction of the attack to the right.
So, the key points of winning against Vendrick would be - anticipate his attacks, stay behind his right leg, and during your window of opportunity, strike him in his back.
Sidenote: If you can, make sure you have Giant Souls for Vendrick. The larger the number of them, the lower his defense will be, making the battle so much easier.