The latest card revealed from Hearthstone's upcoming Curse of Naxxramas set is a new shaman spell: Rebirth. Rebirth destroys a minion before returning it to full health, a spell that will play well with the myriad of new minions with Deathrattle. Rebirth turns any minion's Deathrattle into an on-demand ability for 2 mana -- and puts it back onto the field to be used again. Rebirth could be a terrifying spell even with pre-existing Deathrattle minions such as the Abomination or Sylvanas Windrunner. It could also be used aggressively -- for example, against someone who made the mistake of playing the previously-revealed Anub'ar Ambusher. By destroying your opponent's Ambusher, you could potentially force a far more dangerous minion back into their hand as a delay tactic.
Some of the current mechanics surrounding the way resurrections work (such as with Redemption) means this spell could even be used as a Silence effect. Buffs that have been cast on a minion do not reapply after death, meaning you can easily knock a druid's superpowered tank down to size. It should also be noted that Battlecry effects only apply when a minion is played directly from the hand -- resurrecting it with Rebirth is unlikely to allow that Battlecry to happen a second time.
Some players have voiced concern regarding this card's potential synergy with legendary Leeroy Jenkins. Leeroy is an extremely powerful card right now, particularly in decks that find ways to play it multiple times in a row. A rogue with a pair of Shadowsteps in their hand can attack with Leeroy three times in one turn -- 18 direct damage. More if they have Cold Blood in their hand. A shaman with Rebirth, if Leeroy's Charge ability triggers after resurrection, could now perform the same tactic.