At the end of the Twilight Cathedral you fight the huge demon bat Tiamat. Tiamat takes a long time to kill and take her heart so I suggest buying health potions from Vulgrim.

Frst Tiamat will spit fire balls. When she is doing that, take bombs and throw them at her. When the bombs are stuck on her, use your crossblade and aim at the fire cauldon and then at the bomb on Tiamat, causing the bomb to explode.

She will onto the ground and then you can attack her. When she gets back up she will try and fly and hit you with her claws. After a few times of that she will spit fireballs.

Repeat the step with the bombs a few times (it will take about 5 mins).

Now Tiamat is mad. Now hold the left trigger to lock on. She will charge at you like a bull. When she does that get ready to press "B". If you do that, you punch her and she flies back.

Attack her while shes on the ground from a distance with your crossblade. Soon she will form a ball and drop, causing a powerful wave.

Stay back and jump when she hits the ground so you don't take damage. She does this alot.

Another thing she does is try to claw you. Remember, just lock onto her and run, then her claw will not hit you if you run in the right direction.

Also, at time she will spit fireballs. At first she only spits 1, but then she spits more and more spitting 4 at the most. Just jump/ run away from them and you will be fine.

This battle last for a long time. I didn't time it but I'm guessing 10-20mins. That is why you might want potions (I did without potions but I could only take about 2 more hits).

This does work if you follow this directions correctly!