Backstab is an incredibly efficient early-midgame removal card for rogues. With a Mana cost of 0, it makes a flexible addition to any Rogue deck. This card used to deal 2 damage to any minion, however the 10th October 2013 Closed Beta Patch changed the card to only deal damage to undamaged minions, somewhat nerfing its removal potential towards low health damaged minions. This change provided a big nerf to the card's versatility and synergy with Spell Damage minions, especially in Arena where more than two copies of the Deck card may be drafted and thus played.
In the later game, Backstab is still effective against high Health minions which are undamaged. one cast of Backstab could mean the difference between maintaining or losing board control and tempo of the game. However, it can no longer be used to eliminate damaged minions from play.
Nonetheless, due to its 0 Mana cost and high effectiveness on many 2 Health cards including but not limited to Acidic Swamp Ooze, Novice Engineer, Sorcerer's Apprentice, Knife Juggler and Raid Leader, the Backstab card remains a solid early-game staple in any Rogue Constructed or Arena deck.