Board Thread:Dark Souls II/@comment-72.83.43.51-20140402181657/@comment-184.5.186.240-20140404214359

I'm not on the PS3 so I cannot personally help you. However if you are set on using the ballista to kill the boss, it is possible to parry most of the sword attacks leaving it stunned for long enough to get a shot off. Personally though, since you can tank its attacks I would just recommend getting a fast melee weapon and killing it a slice at a time, poison could also help if you can get enough build up on it.

Hopefully that helps you out.