If you chose to play it face-down, you might lose your bomb to a simple removal spell
Ghostly Dancers and Gremlin Tamer are a great way to stock up on disposable creatures to use in combat, while Victor, Valgavoth's Seneschal can reward you for dumping all your mana into playing and unlocking many rooms per turn
Other trainer cards such as Level Ball can help you search out Pokmon to play that may be deep in your deck
Blaise Zabini and Sirius Black are black characters in HPMOR
Many elemental cards are in this design space, such as Risen Reef and Zendikar's Roil, or even Omnath, Locus of Rage as a heavy hitter
Once you can start generating a lot of mana, you can get set up, but getting to that point might be a struggle because Boros is better in the late-game as opposed to the early game .