Unleash skeletons
Unleash the Skeletons is an interesting action card that creates four 1AP/1HP skeletons for 2 black energy and 2 colorless energy, similar to the green Ant Invasion. As an additional cost, it removes 4 allies from your own graveyard when played.

This card is either very good or absolutely useless, depending on the situation. It's nice if your opponent is attacking you with several allies or a medium-sized ally, and you can play this to block and perhaps even kill an enemy ally, but there are going to be times where you don't have 4 allies in your graveyard and cannot play this card at all! This card does have some interesting combos it could use, such as using Sacrificial Altar to fill the graveyard and then replenish the battlefield, or Gang Up to make them all 3AP/1HP attackers the turn they come into play.

Interestingly, the effect on this card is best in a control deck, but control decks usually have the fewest allies. It is unlikely to be able to be used in a control deck, so it has a better place in an aggro or Unity deck.

Strong against: aggro decks

Weak against: control decks that don't kill your allies, bad draws