I do not have Gather Your Mind, but have put in two Jar of Greeds and a Jar of Avarice, just to make sure my Cerberus gets his meal. Am I alright, or are there better cards?
I'm surprised he did not use Ra's effect to destroy your Cerberus. If he used Sphere Mode to summon out Ra he still has full LP enough to wipe your monsters out.
Also, since Ra was introduced, is it like the actual TCG where you can declare Divine Beast as an attribute and type? If so, there might be some options...
You have options like Abyssal Designator where you force him to discard both his Sphere Mode and Ra into the Graveyard by selecting Divine and Divine-beast.
I use Abyssal Designator with Labyrinth Wall as defense and roughed Marik up easy money. Added Sorcerous Spell Wall / Yellow Luster Shield to make sure his Des Gardius don't go over my wall.