Single-Use Shield

A shield or any other sort of Power Up that goes away after one hit; essentially a One Hit Point Wonder as a power-up instead of a character's default state. As a power-up, it can also provide effects beyond its ability to take an extra hit.

See also Bandit Mook and Mooks Ate My Equipment for things that can treat ordinary armor as One Hit Point Wonders, unlike the rest of the game.

Video Games

 * Sonic the Hedgehog:
 * Sonic collects rings. If he's hit, he loses his rings instead of dying.
 * The shields found throughout the series also qualify.
 * In the first two games, they did nothing more than take one hit for you.
 * In Sonic 3 & Knuckles and the PS 3, Xbox 360 and PC version of Sonic Generations, flame, bubble and lightning shields are available. While they are active, they protect the player from flames, let the player breathe underwater and attract rings, respectively. All three will (at least in S3&K) reflect projectiles without taking damage, but they still disappear after one hit from anything else.
 * The 3D games, the Sonic Advance Trilogy series, and its handheld successors, have two shields available. They both act the same as in the first two games, but one will attract rings.
 * The fan-made Sonic Robo Blast 2 has no less than five such shields available -- the blue Force Shield, which can take two hits; the white Whirlwind Shield, which gives your character a double jump; the green Elemental Shield, which makes you fully immune to environmental hazards; the red Armageddon Shield, which can be detonated to damage everything nearby; and the yellow Attraction Shield, which draws in rings, but shorts out in water.
 * In Ghosts N Goblins and its sequels, the player character's armor disappears after one hit, but they do have the benefit of starting each life with armor equipped. Super Ghouls And Ghosts also offers a shield powerup which can block one projectile attack only.
 * In the Super Mario Bros series, just about any time Mario takes a hit he loses his current powerup (Yoshi, Mushroom, Fire Flower, etc.).
 * In League of Legends, Sivir has the "Spell Shield" ability, which blocks a single enemy spell.
 * In Team Fortress 2, the Sniper's Razorback protects him from a single instant-kill backstab, at which point he has to go back to the resupply room to get a new one.
 * Amorphous: the Reactive Armor explodes on contact with an enemy while leaving the player alive, making him a Two-Hit Point Wonder.
 * The War Craft item Amulet of Spell Shield automatically blocks one negative spell before requiring a 40-second cooldown. Savvier enemies will hit the hero carrying it with a weak spell first, then pull out the harder-hitting attacks.
 * In Crash Bandicoot series, the witch Doctor's mask Aku-Aku protects him (and Coco, etc) from one hit. Picking up another will give you two hits of protection, while grabbing a third will then give you temporary invincibility, which then resets back to two shields.
 * Crash Team Racing however changes it. The Aku-Aku mask is full invicibility, while the actual shield item gives temporary protection from a single attack/hazard, Having ten Wumpa fruit turns the shield green, meaning it lasts forever, so long as you don't take a hit.
 * Final Fantasy X had the "Nul Element" spells (NulFire, NulIce, etc.) which could absorb one attack from the matching element (regardless of strength) when cast, he highest version, "NulAll", combined all four elemental shields.
 * In Odin Sphere, the "Fire/Ice Spirits" potions surround the player with three rotating elemental spirits, which can absorb (and counter) one strike each.
 * Bionic Commando has a pendant, which lasts one stage, and can block a single projectile, but also goes away if you die some other way.
 * The Mega Man series has the Spike Barrier/Shock Step/whatever it's called, which protects you once from the instant-death spikes. But you have to jump to safety before the Mercy Invincibility wears off, or....
 * The Shield orcs in Orcs Must Die have a shield which they drop after a single hit.
 * In The Elder Scrolls IV Oblivion, the Boots of Springheel Jak will prevent you from dying at the end one very, very long fall but are destroyed upon landing. Various exploits exist to survive said fall and still keep the Boots.

Tabletop RPG

 * Dungeons and Dragons:
 * Stoneskin in older editions of Dungeons & Dragons.
 * Module C1 The Hidden Shrine of Tamoachan. A fighter can receive a scroll that gives him a Death Servant. At any time thereafter, if the fighter is about to be killed, the Death Servant will push the fighter to safety and accept the attack that would have killed the fighter. It will only do this once.
 * Several kinds of magical armor in Warhammer provide an excellent armor save but are destroyed the first time they save a wound.
 * This is how regeneration works in Magic the Gathering. Regenerating a creature gives it a single-use shield that saves it the next time it would die. However, even the most common instant-death spells bypass it.

Non-Game Examples

 * In Captain America the First Avenger, the eponymous hero starts off using a triangular shield he picked up during his stage show (a Mythology Gag to the characters' roots). The shield is used precisely once as a guard against the Red Skull's fist. The Red Skull caves it in and it is quickly discarded.
 * Bastille from the Alcatraz Series wears a jacket made from spun fibers of Defender's Glass. It can take one blow that by rights should kill her, but then it's ruined and she has to get another.
 * In Labyrinths of Echo, Magister Honna's headband was enchanted to protect even against One Hit Kill, No Saving Throw artifact weapons. However, it could only do so once, burning up afterward.
 * Reactive armor, on tanks, is designed so that when hit by a shaped-charge...it explodes. It actually works quite well, but the explosives get used up. A lot of anti-tank rocket launchers are now being designed with two barrels—one rocket takes out the armor, the second gets the tank.