All-out

Illusion and reality attacked Seth from everywhere. Thousands of orbs, bullets of mana, energy slashes and even huge waves of mist created by ethereal power crashed into his expansive corrupted area, trying to disperse its power or penetrate it to hit him. 

Some of those attacks were not real, but mere tricks to deceive and distract him, so the real ones could more easily reach their goal. But for the actual Seth, who was just a vessel of his own power, nothing of that really mattered. When anything made contact with his corrupted area, it simply vanished as the energy behind those attacks got absorbed.