COLORLESS ULAMOG, THE DEFILER As much as I dont like Eldrazi, this one in particular seems to be the easiest to abuse in Commander
Being an instant also lets you leverage the ability by holding up countermagic, card draw, or bouncing your opponents board states to remove all blockers before your turn
Honorable Mentions There are enough Robin Hood characters in the game that building a deck around him and Sherwood Forest Outlaw Hideaway is totally feasible
Barrets free equip each combat makes it the more impressive of the two, but both are great support pieces if you feel the urge to go wide with your equipment
With this in mind, it's solid ground from which to launch into the game proper or take things further by making your own decks
On the subject of dual-faced cards, I also accurately predicted that Kefka would show up as one, representing his transformation in FF6