What is Lifesteal in Hearthstone?
Hearthstone has many card effects that are common enough that they get their own keyword - a word or two that immediately tells you how the card works. Let's take a look at the Lifesteal keyword.
Damage dealt also heals your hero.
Lifesteal is a keyword that indicates that when the card in question deals damage by any means, it will heal your hero for the same amount.
Lifesteal debuted in Knights of the Frozen Throne and was the second (or technically third if you count Poisonous) keyword in the game to appear in future sets after its original (first being Discover). It was also retroactively added to Queen of Pain and Wickerflame Burnbristle, making it the second keyword to be retroactively added to past cards (first being Poisonous).
Keywords that Work Great with Lifesteal
Almost anything will work with Lifesteal. Divine Shield or Immune will allow a Lifesteal minion to attack into something without risk of it dying, keeping a threat on the board and will also allow you to benefit from its Lifesteal effect more times. Putting Taunt on a Lifesteal minion will also force your opponent to attack it, resulting in some extra healing. Rush or Charge will also allow you to take advantage of the Lifesteal right away in addition to its usual advantages of attacking quickly.
Playing Against Lifesteal in Hearthstone
Playing against Lifesteal is easier than it seems. Lifesteal minion usually have weaker stats for their cost compared to vanilla minions, meaning they will be slightly easier to kill. If a Lifesteal minion is killed without it dealing damage (such as by using spells), it will also die without it healing you. If you need to use minions or weapons to kill it though, try to use as few as possible to mitigate the amount of healing your opponent will get.
Example Hearthstone Lifesteal Cards
Wickerflame Burnbristle is one of the oldest examples of a proper Lifesteal card in the game, possessing the ability before it became a proper keyword. It combines Lifesteal along with Taunt and Divine Shield, making for a nasty combination of abilities for the opponent to deal with.
Spirit Lash is a spell with Lifesteal, and one of the first cards in the game to use it. It's a simple 1-damage AoE (an area where Priest often struggles, filling a useful space) that will also heal you for each damage it deals, where the healing can stack up pretty quickly. It's an effective Aggro killer especially when paired with Spell Damage.
NetherbreathBADCARDNAME is a card that conditionally has Lifesteal as long as you're holding a Dragon. On its base form, it's not very strong (although serviceable in a pinch). While you hold a Dragon however, it IS very strong making it a surefire pick for Warlock decks with Dragon usage.
Lightforged Blessing is one of the only ways in the game to grant something Lifesteal. You can use it at its simplest form to gain life from an attack, but there are quite a few other ways to utilize it (such as Wild Pyromancer).