this was pulled from PST.org, hope it helps
To start off head to the nearest bomb spawn point and snatch one, aiming towards Tiamat and making sure to stick one to her and not an arch. With a successful throw and placement pull out your Crossblade and aim for the torch and then the bomb on her, be sure to avoid her fireballs see spews out by dashing or air dashing. When she's blown up by the bomb she'll fall down, now's your chance to attack her with about 2 chains of attacks because by then she's getting up and causing a wide counter attack. Now it's time to test your reflex skills because Tiamat is not going to be hovering around the edges of the area instead she'll fly around the background awhile then stop at the edge and come charging at you, she can not be hit by bombs at this point due to the speed she uses causes the bombs to fall off her. After dodging her she'll go back to her usual pattern and you'll blow her up again and hack away. This time when she gets up she stays on the ground, now use whatever means of attacking you want, be sure to dash away from her swipes and far away when she jumps and comes crashing down. Eventually, after so much damage to her, a cut scene will occur and the action finisher will appear for a few seconds above her, if you miss she'll torch you with a fireball and if you're low on health you're dead, if not continue to fight her and dodge her and eventually the death scene will occur automatically.