Seeing as Giygas is comparatively one of the Most Powerful Entities in all of Fiction...I Say you have your work cut out for you, buddy.
Have a quote from TVtropes.net.
>Giygas, the Cosmic Horror Big Bad, proves to be invincible to physical intervention, and then to divine intervention. He is defeated only by the intervention of YOU, the player, because even an all-powerful Cosmic Horror like Giygas is still nothing more than a bunch of pixels and binary code to you. That's right, YOU are Cthulhu.