Use Golden Castle of Stromberg Hexe Trude for on-demand removal, and to banish cards for Gren Maju. Orochi is mainly for banishment and stalling (though it can also be used with Hexe Trude to Xyz Summon a Rank 8.). Eater of Millions for easy removal and high ATK late game. The rest is mostly negation or draw cards.
Megafleet Dragon is in the ED in case you go against a Cyber Dragon deck.
(note: despite the goal of using Gren Maju for high ATK, I find myself winning with Hexe Trude much more often, due to the inconsistencies of Gren Maju. Don't be afraid to simply swarm with Hexe Trude to win.)