this is a simple fight, a 5-man required to unlock the raid, and giving an introduction to the Wardens.
When you enter, you will see the two wardens chined. The mysterious man who captured them releases the Fire Warden on the group, promising him freedom in exchange for 'an entertaining fight'. Before he attacks, though, the man mutates the Fire Warden into some kind of monstrosity. The fire Warden has an occasional knockback as well as stomp, but aside from heavy damage, is not tough. When he reaches 50%, the man will get bored and return him to his place. Instead, the man will release the Frost Warden.
The frost warden is unwilling to serve the man, but the man activates the warden's frost aura. Simply stay out of the aura for 30 seconds (the warden moves) for the man to get bored once more and send the Frost warden back.
This time, he sends both wardens at you. The wardens decide that they should not focus on the players, but rather on their captor, and shatter the chains that were holding them, causing their captor to flee. Out of gratitude, the wardens allow you to live.