Try to leave Frozen Eleum Loyce for the cathedral, and you'll be attacked by an invisible boss. But once you've obtained the Eye of the Priestess, you can take on this massive jungle cat: Avaa, the King's Pet.
Avaa isn't too difficult to defeat, but she (I assume she) is constantly on the move. You'll have to attack just after dodging--before she leaps away. The basic attacks are swipes of her claws, or a lunging swipe from further away. These are easy to block or roll under.
She may also charge up her paw and slam it into the ground, causing deadly ice crystals to erupt upwards. Keep your distance to easily avoid these. If she seems to tense up, keep your distance again, as she is about to unleash a burst of energy.
Occasionally, Avaa will summon a group of ice crystals in the air in front of her. They are ice-based, so using your shield will result in some chip damage. You can sprint away from the crystals as they home in, however. Even less frequently, she will do a biting attack--roll away, or you'll suffer a bunch of chewing damage.
Avaa isn't difficult to defeat, though you'll have to be quick on your feet to give damage and avoid taking any of your own. This fight shouldn't take you too long.
For more help be sure to check out our complete Dark Souls 2 Boss guide.