2 Marchesa, the Black Rose I like Marchesa so much that I've already published a Commander deck built around her
Flower Selecting lets you take a look at the top two cards in your deck and put one of them into your hand - the other goes in the Lost Zone
Master Duel has an entire system that allows you to create new cards, saving you the fuss of opening booster packs
Enchantments that either have abilities that trigger when they are destroyed, like Hatching Plans, or those that have worn out their usefulness, like Treacherous Blessing, are great inclusions for Ertai
Lastly, the deck should include spot removal to take out legendary creatures like enemy commanders, making it easy for The Balrog, Durin's Bane to attack its enemies directly and deal commander damage