The only move that is really a threat from sif is his double spinning attack. That move destroys everything.
Other than that he is very straightforward and not too big of a deal. He is quite fun though, and is pretty much a very small taste of what the DLC is like.


EDIT:
Oh, and Ultima... Here's a slight tip for that little black knight sword of yours.
If you can find a certain glowing lizard... do not let it escape. Hunting these lizards is the key to unlocking that swords potential.
Also: Buy the weapon/armor upgrade boxes, and the repair box. You will need them.