This is a delayed AOE with a number of restrictions. It's similar in theme to Corruption, although a lot easier to play, since you can cast it on a minion then kill that minion immediately after. Your opponent can play around it through good placement of their minions, particularly since it isn't effective unless they have three minions out.
We all know how much Priests love to use (and sometimes borderline abuse) their hero power to keep themselves and their minions alive - well this card can help you depending on how much you've used your hero power! Though it is rather slow at 7 mana, it's quite versatile, a late game card able to be used as both mass aoe removal AND a powerful finisher.
Auto-Attack works just like the chess game, with your board dealing damage to the one or two minions directly across them. Your minions take no damage. With a bit of foresight into board positioning, this gives every minion on your board a personal AOE.
This card is good for priest without being too broken as most priest cards have low attack value, but this allows them to get extra value. It also would allow cards with can't attack to be used without the help of Purify.
About time this iconic spell existed in Hearthstone. I could change the wording (effect is still the same) to "Deal 2 damage to a minion, 1 to adjacent minions and 3 to the enemy hero" but I like the 3-2-1 progression as it's much more flavourful.
Priest need more board clear! The general idea is that the Life Bender convert life (health) into fire that destroy the enemy. While she obviously good in Priest, Alexstrasza can also be used in Control Paladin that run Lay on Hands and Forbidden Healing or even Reno Jackson decks for 15+ damage after healing with Reno.