Life Drain

It's basically an attack that does damage and also heals you.

Life Drain attacks generally come in three flavors:

HP restored equals the full damage dealt. Sometimes the reverse is also true, causing the maximum strength of the attack to vary inversely by the user's HP, and in particular fail to have any effect if their HP is already full.
HP restored equals a reasonable portion of the damage dealt, frequently 50%.
HP restored is a small fraction (such as 1%, 10%) of the damage dealt, to the point where the HP restoration is more of an added effect than the primary purpose for the attack. May also manifest as a status buff.

Oftentimes, Life Drain will be ineffective against undead (since they don't have any Life Energy to drain), or worse, it'll end up healing them and hurting the user, for much the same reason that Revive Kills Zombie.

Subtrope of Liquid Assets. Related to Mana Drain and Level Drain. For the non-video game mechanic version, see Vampiric Draining.

Examples of Life Drain include:

Collectible Card Games

A staple effect of black spells in Magic: The Gathering, as well as white spells such as Spirit Link (which tend to emphasize the healing portion of the effect; Spirit Link takes something that automatically does damage—creature combat—and makes it heal you too).
Yu-Gi-Oh!

Tabletop Games

Dungeons & Dragons 1st and 2nd Edition.
- A Half-Human Hybrid-succubus (alu-fiend) can drain 1d8 Hit Points by touch and be healed for half the amount drained.
- A Vampiric Regeneration Ring heals its wearer for half the Hit Points the wearer inflicts on other creatures in melee combat.

Video Games

Pokémon has Absorb (as well as its upgrades, Mega Drain and Giga Drain), Dream Eater, Drain Punch, Horn Leech, Leech Life, and Leech Seed.
- Pokémon, for its worth, has all three types. "Dream Eater" restores full damage, "Absorb" and family restore half, and the "Shell Bell" hold item (activates whenever an attack successfully connects with the foe) restores 1/8.
- The Big Root item can increase the amount of damage restoration when held.
- The ability 'Liquid Ooze' (possessed by Tentacool, Gulpin, and their evolutions) causes any HP-draining attacks (aside from Dream Eater) used against the wielder to instead cause damage to the drainer (though the damage itself is not negated).
Underdark spells in Fun Orb's "Arcanists" specialize in draining life.
Team Fortress 2 has several variations:
- The Medic's Blutsauger and Soldier's Black Box heal set amounts of health whenever they do damage (for the latter giving it several times if the Splash Damage hits multiple enemies).
- With a kill, the Pyro's Powerjack restores a set amount of HP, the Demoman's Eyelander boosts max HP a set amount, the Half-Zatoichi restores all health, the Spy's Conniver's Kunai absorbs all the HP of whoever he backstabs with it (though it maxes out at 180), and a Scout with a Candy Cane on him drops a health pack (even if he doesn't get the kill with the Candy Cane).
- All attacks against enemies covered in the Scout's Mad Milk or by people under the effects of a nearby Soldier's Concheror restore a percentage of the damage they deal.
Diablo. One possible weapon special ability is healing your character when you damage opponents.
Sonny 2. A number of attack abilities (such as Terrify) damage an enemy and heal your character.
Dragon Age also features a Drain Life spell. If you cast a Vulnerability Hex on the target first, you can actually perform an Improved Drain.
Knights of the Old Republic has a dark-side ability with the same name.
Most Final Fantasy games have the spells "Drain" and "Osmose," which respectively drain HP and MP, and usually restore one-to-one. They vary substantially in power from game to game, or even between remakes, but are usually pretty lame compared to spells that just heal or just hurt.
- "Osmose" fits this trope perfectly as it is usually good more for being able to restore MP to the caster than for any serious effect on the enemy. "Drain" is usually a decent mid-level spell than supplement a weak healer (or lack of any healer) in the party. If either have any kind of "shadow" element attached to them, be very careful about casting on demons and/or undead. Can result in a reversal of Revive Kills Zombie, healing the enemy (or restoring their MP) at the cost of damaging the caster (or draining their own MP)
  - Osmose (absorbs MP) and Rasp (damages MP) in Final Fantasy VI became vital in several parts of the game, namely the Floating Continent and the Tower of the Magi. Some monsters relied on magic and by reducing their MP to zero, they die, which may be easier and faster this way than to fight them normally by damaging their HP. Of course, this usually flies over the heads of many players if they didn't talk to a certain NPC that explains this tip.
- It's also common to have one or more weapons that do the same—usually a Blood Sword—which may or may not be game breaking if used in certain ways.
  - In Final Fantasy VIII, that effect could be achieved by junctioning the Drain spell to a weapon's Status Attack, with the percentage of damage added to the character's HP based on the number of Drain spells stocked (up to 100 for 100%). As with most spells in the game, this was usually better than actually casting it.
- Final Fantasy Tactics had these spells always take a percentage of the target's maximum hit points or magic points, respectively, ignoring magic defense. On enemies that had very high defenses and a large stash of hit points (like all of the Lucavi and the Final Boss), they effectively became the most powerful attack abilities available, taking them from Not Completely Useless and turning them into a Game Breaker.
Necromancers in Guild Wars have a large selection of spells that do this.
One of the special abilities of the Chain-Rod weapon in Mega Man Zero 2.
Edge from Atelier Iris 3 can use Soul Eater when equipped with Jiptus Mana. Iris can summon the Faustus Mana to do the same, but since many of the enemies are immune to Faustus' trait...
RuneScape has quite a few: Onyx-tipped crossbow bolts, the Saradomin Godsword and Saradomin/Guthix Bow, Guthan's armor set, blood spells, and the Soul Split curse.
The Drain Rune from Suikoden series will heal its bearer's HP by 10% of the physical damage done to a single enemy.
One of Beat's guns in Eternal Sonata restores his health as a percentage of damage dealt to the target.
The 7th Saga featured two spells, HPCatcher and MPCatcher, which transferred some of the targets HP or MP to the caster.
Reave (Samara's bonus power) against organic enemies in Mass Effect 2. Related is Energy Drain (Tali's bonus power), which does the same thing to synthetic enemies, though it restores shields instead of health. Both return as bonus powers in Mass Effect 3 (Energy Drain again as one of Tali's powers; Reave as one of Kaidan's bonus powers), but Reave has been nerfed so that it reduces damage taken instead of restoring health, making it no longer an example of this trope.
City of Heroes had various life drain powers in its Dark themed sets. They ranged from Siphon Life, which heals a small amount of its damage dealt, to Dark Regeneration, which deals very minor damage in return for the strongest healing in the game.
- The Water Blast power set, added late in the game's life, had "Deydration". (Which, oddly, worked just fine on robots, sentient fireballs, and other opponents unlikely to have water as a major component of their bodies.)
Heretic granted life draining ability when the Tome of Power was used with the gauntlets.
Dark Rangers in Warcraft III can learn a Life Drain spell, which steals HP as long as it's continually channeled. Dreadlords can learn Vampiric Aura, which gives a draining effect to friendly melee units' attacks.
Warlocks in World of Warcraft have this spell outright; several of their other spells, such as Corruption or Unholy Affliction, will grant a smaller percentage of health back per damage inflicted.
- Death Knights have Death Strike, an Unholy ability which heals them as it damages the enemy. Warriors have Bloodthirst, which has a similar effect, but without the Dark Magic lore explanation.
Vampires in the Heroes of Might and Magic games gain 50% of the damage they deal on an attack back as HP.
Champions Online has "Lifedrain" as a rather potent such power for the Darkness power set. And when used by NPC's, it's backed up by the Badass Boast , "Your soul shall be mine!"
The later Castlevania games give you access to HP-draining abilities. The Succubus soul in Aria claims to let you drain HP from enemies with your attacks, but what actually happens is that every time your weapon hits any enemy or object (including all those destructible candles and things), you regain 5 HP. In Dawn the Succubus soul is a subweapon, with which Soma steps forward to bite enemies, drinking their blood to restore a healthy amount of his HP. The close range required to use this makes it hard to top yourself off without bumping into the enemies you're trying to drain.
- Before that, Alucard had Soul Steal in Symphony of the Night. This was probably the easiest way to kill Beelzebub.
Warhammer Online has a large selection for a variety of classes - mostly healers, who get spells and tactics that heal when dealing damage such as a tactic granting a straight 25% of damage dealt returned as healing to your defensive target; specific abilities that deal damage and give back healing at 50%, 100%, 150% or 350% of the value of the damage dealt; or other, more esoteric methods (a removed ability for a Zealot was to place a debuff on an enemy that would last 60 seconds, and transfer life every 5 seconds). However, melée classes also have abilities to steal life and either bolster themselves or, in the case of tanks, the person they're guarding.
Present in a few ways in Dissidia Final Fantasy: The special ability granted to Firion and The Emperor in their EX Modes is Blood Weapon/Blood Magic respectively, functionally identical—when they deal HP damage, they are both healed to an amount equivalent to their Bravery stat when performing the attack. Kain's EX Mode in the prequel gives him access to a move named Lancet, which will heal Kain equivalent to the damage dealt.
- It should be noted that the Blood Sword equip in the original Final Fantasy II didn't actually function this way; back then, it caused damage proportional to the maximum HP of the target, and did NOT restore any of the wielder's health. It was only from Final Fantasy III that the 'drain HP' effect was attributed to Blood weaponry that appeared in subsequent games.
- The summons Barbariccia and Kraken work kind of like this, as well—their effect is to swap the Bravery of the caster and the opponent, ideally crippling the opponent while giving the caster a hefty total of Bravery. However, considering that Barbariccia's effect activates upon the opponent using their own summon and Kraken has a countdown of significant length before taking effect, they also have the potential to backfire in a spectacular manner.
Fire Emblem: Path of Radiance/Radiant Dawn had the spell 'Nosferatu', which, oddly, is a Light element tome, as well as Sol, the Occult ability for the Paladin class. In previous Fire Emblem titles, 'Nosferatu' was a Dark element spell.
Appears in just about every Shin Megami Tensei game, in the form of spells such as "HP Drain", "MP Drain" and "Leech" ("Meditation" in SMT: Nocturne) (which simultaneously drains HP and MP).
In Scarface the World Is Yours, Tony regains health when he kills enemies in Blind Rage.
In Sword of the Stars the System Killer will regain health if it survives or wins a tactical encounter in a system.
'The extractor' from Project Eden drains life energy to recharge your energy reserves, extra energy creates batteries for your team to use.
Shuma-Gorath has a throw that does this in his appearances in Marvel vs. Capcom; it started out being able to take all life but eventually was downgraded to only restore Shuma's 'red' life. Thanos also has a super that can drain life in his two appearances.
League of Legends has lifesteal and spell vampirism, which regenerate health based on attacks and magic damage respectively. These characteristics are mostly given through items, but Nasus has lifesteal and Morgana has spell vampirism as passive abilities. Beyond this a number of champions have spells that do this in various ways.
- Fiddlesticks Life Drain spell is a damage beam that restores a significant portion of the damage dealt as he channels it.
- Vladimir has two spells that drain health; Transfusion is a single target attack, Sanguine Pool involves sinking into a pool of blood and draining the health of those he passes underneath.
- Nunu's Consume deals a huge amount of damage to a non-champion target, and heals him.
- Skarner's Fracture deals damage and places a mark on those it hits. If he hits them before the marks wear off, he gets healed.
- Sion's Cannibalism temporarily gives him an extremely high life drain that heals all nearby allies instead of just him.
- Trundle's Agony steals health, temporarily increasing his maximum and decreasing the target's.
- Warwick's normal attacks heal him, the amount increasing as he hits the same target. His Hungering Strike also heals him for part of the damage done.
In Dark Souls, the curved sword Server grants a little health with every hit.
In Barkley, Shut Up and Jam: Gaiden, Barkley can learn Vampire Dunk which hits an enemy and heals Barkley for the amount of Hit Points damaged. Later there's a Bonus Boss' skill Soul Consume, which combines this with a One-Hit Kill.
In Wizard 101, this is one of the Death School's specialties - healing the caster for half the damage dealt to the opponent(s). They can also do this in reverse to heal themselves or allies, speed up the preparation for stronger spells, or even boost the attack power of spells.
Skylanders: Spyro's Adventure has Chop Chop, who gains the ability Vampire Blade upon leveling up. It allows his sword to steal health from enemies.
In Command & Conquer: Red Alert 3, the Soviet faction is likely the only non-magical military faction to utilize this attack. Their Main Battle Tank, the Hammer, utilizes it as part of a secondary ability, and a faction-wide upgrade called "Grinder Treads" lets the Hammer, Apocalypse and other tracked vehicles recover health by running over enemy infantry (or tanks for the Apocalypse).