Try this strategy: accumulate a lot of allies in your graveyard, play Sacrificial Altar and Monster Mage. Have at least 4 black and 2 normal energy in store (this strategy would have to take place late in the game), create a Monster Ally, and sacrifice it to damage your opponent! Do this four times (or five, if your opponent is healing themselves) and you've won the game! If you've got a Soulseeker out, this'll make him stronger as well-- each Monster Ally you sacrifice will give him +1AP/+1HP to crush your opponent with.
Strong against: Decks that populate your graveyard, be it because of your opponent or yourself doing so purposefully.
Weak against: Burn decks, as well as the ever-imposing Killer Wave.