Gravity can bend light. So, what were the magical attacks before it?
Sylvester knew that very well and used his vast array of skills to his advantage. While focusing on derailing Raz's strike, he focused all his magical power on increasing the effects of gravity on Julius's body. Since it worked on the Demon Zama'tar, there was no doubt it'd work on Julius, too.
Shwooo!
Julius found his body dragged straight down into the sea, while the bone blade on Raz's arm was blocked by Sylvester in a resounding exchange. Sparks flew, and Sylvester quickly countered, swinging back at Raz.
Clash!
Raz used his own skull to block Sylvester's strike and hit back with his bone spears that instantly grew from his ribcage.