Continue your journey with Prima's Dark Souls 2 Guide and Walkthrough!

Reward: Guardian Dragon Soul

There's one simple strategy that works extremely well against the Guardian Dragon: stay by its hind legs. This avoids the Dragon's grounded fire breath attacks, and the swiping attack from its mouth. If it lifts one leg up, move away slightly to avoid the stomp, then move back in and continue attacking.

If the Dragon takes flight but hovers over you, move away to avoid the ground stomp that follows. If the Dragon flies to the side of the area, move as far away from it as possible to avoid the long-range fire breath that follows. While you can remain directly under the Guardian Dragon to avoid the fire, you will still get hit when it lands and stomps the ground. If you stay on the far side of the area, you avoid the fire breath and the ground stomp that follows. 

When you move back into close proximity, be mindful of the Dragon's various close-range attacks. If you approach from a distance, the Dragon may attempt to bite with its mouth or breathe fire straight ahead. If you're not quick, either attack may occur before you can get under the Dragon to attack its legs. Dodge to the side to avoid the fire breath, and dodge forward or backward to avoid the swiping attack, depending on your distance from the Dragon. If you're close enough to dodge under its legs, dodge forward. If not, dodge to the back.

Take down the Guardian Dragon, then head through the doorway and across the bridge. Go down the hallway and pick up the Dragon Scale to the right of the doorway. Move into the lift to reach the floor above, then head through the doorway to the right and down the hall to reach Dragon Aerie.