These are cards that don't fit into any of the other categories.
Vengevine: To get this all you have to do is play 2 creature cards. Kinda hard in a deck without land. Often times multiple Vengevines will win you the game because they have haste. In some games it will just stay in the graveyard for the whole game while other times it's a game winner. You have to cast the creatures to trigger Vengevine so the only thing that will trigger this will be Ornithopter,card:memnites, and Salvage Titan.
Salvage Titan: A 6/4 body for sacrificing a mere 3 card:ornithopers? Deal! This is the only card with a mana cost of more than in this deck that you will be technically casting. Some games you will just return it from your graveyard to your hand in order to discard an additional card that turn. That's especially helpful if you have a Prized Amalgam or Vengevine and a dredger and you don't have any dredgers in the graveyard. Then you can discard a dredger and that card.
Hollow One: After the banning of Faithless Looting this card lost its deck. Usually to play Hollow One you will discard a Phantasmagorian and then discard three cards to return Phantasmagorian to your hand. Making Hollow One cost -1 mana. Street Wraith can also help lower its mana cost.
Prized Amalgam: Just a 3/3 you get at the end of your turn if you milled a Narcomoeba or returned a Vengevine to play. Sadly you don't immediately return it to the battlefield but it's still good.
Sword of the Meek: A great card to sacrifice to Salvage Titan or to make your card:narcomeobas bigger. You can also exile it from your graveyard to help get Salvage Titan back to your hand.