It is highly recommended to have 3 knights killing in order to break its shield.
For solo hunting it is recommended to be level 130+. Use Fierce Berserk as often as possible as there is a time limit of two minutes inorder to kill it. Remember that with its high resistance to physical attacks, even a skilled knight can only do 150 damage on average with Fierce Berserk. It's not likely that you can kill more than one within the two minute time frame. Keep in mind that it paralyzes often with its Wrath of Nature attack, so its wise to heal every turn so that you can stay diagonal and avoid the lethal energy beam.