"But I suddenly scream "Shit!" Because my guy has just been hit With my hits points indicator less than full
But it's quite inconsequential And my wrath will be torrential For the following one second I am in-vin-ci-a-ble"
— The Gothsicles, "One Second Ghost"
One hallmark of the Platformer is Everything Trying to Kill You, and this killing is usually done by the simple act of touching the player character.
Since this collision is injurious to the player and harmless to the attacker, even if the player is permitted more than one injury before death occurs, he might quickly deplete his entire Life Meter before being able to disentangle himself from the enemy.
As a small mercy, most games that work according to these rules grant the player a small span of invulnerability whenever damage is taken, giving him time to extricate himself before another hit can be taken. This is visually indicated in most games by partial transparency or flashing of the player sprite. The momentary invulnerability may be substituted for (or coupled with) the player character being physically thrown backward from the point of impact. If the player isn't knocked back and takes different amounts of damage from different attacks, there may be situations where a player can deliberately run into something that deals little damage and use the Mercy Invincibility to run past something more dangerous.
Enemies, particularly bosses, will often have this as a guard against the player Button Mashing and/or rapid fire controllers, which affects the overall length/ease of the fight.
Fighting Games, especially 2D fighters, have a version of Mercy Invincibility where a character receives a couple frames of immunity after he or she is knocked down. This allows the knocked down player to get up without having to worry about being hit while his or her character is down. Another, related ability to that is the Recovery Attack, where a character, while not necessarily being invulnerable, may be able to fight back.
A similar function can be found in most games that have Random Encounters. Rather than having a purely random system (which can often lead to encounters at every other step), there will be a built in minimum delay between each encounter. This is to prevent a situation where an encounter at every other step overwhelms the players. More modern games may even give you a coloured indicator that starts flashing as the next random encounter approaches, giving you time to chuck some health potions at your party.
Very common in all kinds of Platformer. Shoot Em Ups also have this, typically after losing a life, giving your new life a chance to position outside of enemy fire. Occurs much less commonly in the First-Person Shooter. Many Speed Run strategies exploit these invincibility frames for more efficient maneuvering.
Compare Invulnerable Attack.
In Star Control 2: The Ur'quan Masters, an encounter would normally be triggered whenever the player's flagship touched another spaceship on the map screen, but for a short period following an encounter the player was able to pass by any number of ships without another encounter resulting. This prevented an immediate re-encounter with the same ship, but was also useful when the player was being swarmed by dozens of hostile fighters. The encounter-free period was signaled by the non-player ship flickering.
However this does not work in the main screen, and is one of the reasons the probe enemies are so dangerous. If the probes are not down by the time you start messing around in Ur-Quan space you can get stuck in a loop very easily of fighting one of the two Ur-Quan, then a probe, then another Ur-Quan.
Both player characters and enemies alike in Dragon Valor have invincibility after being struck.
Goof Troop has invincibility for a second after getting hit.
Most of the games in the Zelda series have this as a mechanic for Link, but not for his enemies. After taking damage, Link cannot take damage again until a specific period of time has elapsed, though this time period is usually quite short.
In The Legend of Zelda, both Link and his foes have mercy invincibility, but Link's lasts longer. You can swing your sword as fast as you want, but enemies can't take damage that fast. Thankfully, neither can you, even if standing on top of an enemy who causes Collision Damage.
In The Legend Of Zelda II, Link has a slight period of invincibility after being hit, but this also comes with being knocked back by the hit. It is rather hard to abuse mercy invincibility to gain distance in this game unless your LIFE stat is absurdly high.
In The Legend of Zelda: The Wind Waker, some enemies do have mercy invincibility as well, and this depends on how and what items you hit them with. Most enemies can be knocked down with a jump attack, but this also affords them the ability to get back up without being vulnerable to you.
Double Dragon had this, and allowing yourself to get hit was actually one of the easiest ways to get past certain booby traps.
The Streets of Rage series has a unique take on this. Like all other beat em ups, your character cannot be hurt while they get up after being knocked down. However, when you lose a life and respawn by falling from the sky, all enemies, including bosses, on the screen are knocked down in order to prevent the enemies from ganging up on the player that just spawned.
A lot of other beat'em-ups have it as well. Some of them knock all the enemies down with no visible explanation for it like So R, while others do stuff like having your character's respawn trigger a local missile strike, like in Cadillacs and Dinosaurs.
Dragon Ball Advanced Adventure gives you a moment of safety if you get hit a strong attack or multiple small ones in a row, but the bosses also get a form of it. After you hit them enough times in a combo, once you stop juggling them they'll flash blue for a few seconds. While they're flashing, your attacks will connect for no damage at all, indicated by a dull "thunk" with each hit. This can be abused by first knocking the enemy into the air with a Launcher Move and comboing them to death before they hit the ground to screw them out of their Mercy Invincibility, although this can be extremely hard to do outside of a TAS and isn't really possible to do at all in VS battles.
Many racing games have a "reset" feature that puts your car back in the road after the player runs into an unfortunate accident; most of the times, after the player presses the reset button, the car will flicker for a short time, during which other cars will simply clip through the player's car.
Although Need for Speed games feature this ability, Most Wanted, Carbon, and Undercover have actually made it less useful. Considering the fact that there are two situations where resetting would be useful (flipped over car and tires shredded from a police spike strip), the first instance has the car reset automatically, and late in the game, such a situation means you've probably lost the race anyway. The second situation, where the player's tires have been shredded (preventing a getaway as the car simply will not move), seems like it would be useful, but the reset inevitably places the car in the middle of the pursuing police with no velocity, resulting in an arrest before the player can do anything.
And Hot Pursuit makes it useful in a completely different way. Destroying opponents or hitting them with a weapon causes the camera to pan over to the crashing vehicle. Meanwhile your own car drives on autopilot and is invulnerable until you regain control. This can lead to interesting strategies in multiplayer: you are down to 10% health and an EMP is locking on to you? Wreck or spike strip a random opponent and the EMP will fail.
Almost all the Mario Kart games gave you this after being attacked which effectively prevented a player form being hit multiple times in a row. Mario Kart Wii is the only exception and has been cause for many gamers to call the game the most unfair game in the series.
This only applies after you have finished landing in MKDS, so you can red shell someone, then run into them with a mushroom in battle mode and (usually) get an instant kill.
Mario Kart's mercy invincibility issues stems all the way to Mario Kart 64. Spinning out doesn't make you immune to further attacks that can make your character tumble against the track (usually caused by shells). However, being hit by a shell or similar items makes you tumble but immune to being hit again by any other item (except the thunderbolt). Mario Kart Wii's issues is magnified due to all the items designed to screw over everyone at once plus 12 racers using items everywhere.
In Super Smash Bros.. Melee, a character who reappears after being knocked out is invincible for five seconds. This can get very annoying in "super sudden death" matches.
In Brawl, however, you have invincibility for about 5 seconds, or until you move, so if Olimar uses his Final Smash, you won't be killed twice.
Also, Brawl allows immunity after getting knocked down and when you grab an edge.
The Gundam Vs Series has a Down Value (DV) associated with each attack; when someone's DV hits 5, they instantly get knocked down and can't be hit again until they stand up. This means the player has to carefully mind what attacks he uses, lest he waste a big attack because he built up the opponent's DV too high before launching it.
Cosmic Break uses a similar damage reduction system for consecutive hits over a short period of time, although how much damage reduction will be granted is determined by a bot's toughness (TGH) stat.
Like a lot of fighters, Dissidia: Final Fantasy uses this to let characters who have been Punched Across the Room or knocked over recover and get back in the fight. However, unlike a lot of fighters, this is averted in the sequel, Duodecim. Yeah, you can't whale on your opponent further after you've nailed them to the wall—but your Assist Character can. And if your assist was the one to do the wall-nailing, then you can gladly continue the damage. This is the main way players unleash combos in that game.
In PlayStation All-Stars Battle Royale, a player that's taken a certain amount of damage in a single combo (which is to say, have given their opponent a certain amount of AP) will fall out of the combo and receive invincibility till they can touch the ground. Since this includes invincibility to Supers, players have to time how they go about launching one during a combo.
In a variation, Crysis has the North Korean foes stop firing on you temporarily when you drop to critically low health.
The Battlefield series kind of has this with the critically wounded state, you can't be finished off like in Enemy Territory by normal gunfire but an explosive weapon will turn it to a "kill" where your helmetless body disappears.
The Custom-TF Quake mod had a purchasable "Respawn guard," preventing all damage for about 3 seconds after you respawn. It's tied for the least expensive upgrade (at 25 points, out of usually around 10,000), so almost everyone gets it.
Golden Eye 1997 for the N64 played this straight, providing about half a second of invulnerability to the player after being damaged to make it easier to survive and escape a fierce gunfight. This somewhat nerfs the impact of automatic weapons, especially in multiplayer.
Its spiritual successor, Perfect Dark, did not do this, despite being built from the same game engine as Golden Eye 1997. Closing in on an enemy in PD and letting him shoot at you (not close enough for him to melee attack you instead) could be severely damaging or immediately fatal on the harder difficulties, as the foe's accuracy on you would greatly increase from being that close, and each and every hit would damage you.
Drakengard has this: the protagonist can take three hits in succession before falling over. When he gets up, he has about seven seconds of invincibility to do with what he may.
In Phantasy Star Online, players would be knocked down and receive a short mercy invincibility period as they stood up again if they took more than a certain percentage of their max HP in damage in a single blow. This led to an absurd situation in which certain characters with more HP and higher levels were in fact, less survivable than low level characters with less HP, and many players simply minimized their HP and defense stats on purpose to make use of this.
And then Ultimate difficulty messes with this by taking away allMercy Invincibility if you don't get knocked down. The Mines are perfectly set up to take advantage of this, as now all those double attacks and Macross Missile Massacres hit in full force.
In City of Heroes, self-revive powers have a brief period of complete invulnerability for a moment or two after pulling yourself off the floor. Also, a character revived by any means will be protected from XP Debt (the game's penalty for being defeated) for a short period of time, to allow a character to be revived without risk of being penalized twice if they get defeated immediately after rezzing.
Pretty much every incarnation of the Mega Man games has had this ability. Some of them actually had items that would extend the length of time it was active. The invincibility actually made it advantageous to be hit in certain spots. In most Mega Man games, touching spikes means instant death, but hitting an enemy right before hitting spikes would allow you to escape with your life (provided, of course, you had time to extricate yourself from the spikes before the invincibility wore off). However, this doesn't apply at all to Mega Man 1. Touch spikes at any time, even after getting hit? BOOM!
By the way, almost every single boss in the Mega Man series has Mercy Invincibility as well.
There are a few times where you can exploit mercy invincibility to get items earlier than you should be able to, especially in the Mega Man X series. For instance, in the second game, the Heart Tank in Wheel Gator's stage is above a wall of spikes. Normally you would have to use the charged Speed Burner to fly over to it, but if you goad the nearby enemy into firing a shot to the left, you can get hit by it, then scramble up the wall while still flashing from the hit.
Inverted in Mega Man & Bass, where bosses get LONGER mercy invincibility than the player character. The real kicker? Bass's primary weapon is a weak rapid-fire shot. However, only the first hit will count for anything, meaning any boss fought with Bass' default weapon takes much, much, much longer to kill than it should.
Spark Mandrill in Maverick Hunter X doesn't get Mercy Invincibility. If you use Shotgun Ice, you can hit him again right after he thaws out, letting you defeat him before he can do anything.
In Mega Man 1 the invincibility expires even when the game is "paused" with the Select button (different from the weapon select screen, and only present in that incarnation of the game); hitting Select immediately after hitting a boss allows a subsequent hit to strike the boss straightaway. This is what enables the Elec Beam/pause rapidly glitch that can kill a boss with one or two shots.
In Mega Man 10, the reason the Triple Blade is so powerful at point blank range is that each blade counts for a separate hit, thus letting you hit an enemy for 3 hits before Mercy Invincibility kicks in.
Mega Man Zero has an interesting variant - while both the player character and bosses normally have mercy invincibility after getting hit, Zero's primary weapon will actually ignore a boss's invincibility if you go for the full three-slash combo.
For the X games in the PS1 era, bosses have a very short invincibility period after being hit by X's buster, allowing him to deal damage at a much faster pace. As a downside, bosses now have much more health (In X5 even, they have life bars that stretch the entire screen). They still get full invincibility when you hit them with a charged shot or they weakness, however.
In Rockman 4 Minus Infinity, one boss does not have Mercy Invincibility: the first form of the Wily Machine. Given that it has 784 energy, 28 times the regular amount, this is most definitely a welcome change.
In the case of Super Mario Bros., this can happen to powered-up Mario or Luigi, resulting in the loss of any special ability he had.
Super Mario World had some castle sections involving reciprocating spiked pillars, which seemed to ignore Mercy Invincibility; the game treated them as moving walls, meaning they could squish the player against the floor for an instant kill.
Particularly difficult Super Mario WorldROM hacks will sometimes have sections of their levels that are impossible to get through unless you're invincible, so the designer will throw in a powerup just so you can lose it and use the Mercy Invincibility to race through these sections. If you don't make it in time, you die.
New Super Mario Bros. plays this straight, except in one surprise case: as every Super Mario Bros player knows, if you meet Bowser while powered up, you can just run right into him, take a hit, and use the Mercy Invincibility to continue on to the goal. But in NSMB, deliberately running into the final Bowser hurtles Mario back across to the left of the screen. This is, perhaps, the cleverest part of the whole game.
Which doesn't keep you from saving a giant mushroom, grow large, and land a one-hit-KO on him by jumping on his head.
In the remake, the boss fight with the giant eye-monster Viy averts this - standing on its body will rapidly drain your health, with no Mercy Invincibility.
Vectorman had an interesting form of this. When you get hit, you keep your invincibility longer if you continue getting hit (by an enemy, lava, etc.), and further, if you keep ramming the minor enemies, THEY get destroyed. Sweet.
The Metroid series always has mercy invincibility. However, it lasts much shorter than it does in some other platformers, to ramp up the difficulty. A glitch in Super Metroid allowed you to have a permanent Speed Booster effect (which combines Super Speed and Invincibility Power-Up in one convenient package), but it had the unusual side effect of eliminating Mercy Invincibility - making spiked floors, normally an inconvenience at best, your worst nightmare.
Super Mario 64 had a slight aversion. In Lethal Lava Land, if Mario falls in the lava, he takes damage and goes flying but doesn't get the Mercy Invincibility. If you're not careful, you can be killed very quickly.
Bypassed by a special kind of damage called "Hazard Damage" in MaelstormM's flash game, Mega Man X Next. With most things that can hurt you, you just lose a bit of health and turn transparent for a moment to indicate how long until you can be hit again. However, there are many things which will consistently deal Hazard Damage even if you're still transparent from another hit. This includes at least one attack from every boss's arsenal, and the damaging hazards in the levels. To make up for this, you don't flinch from any hit no matter how powerful it is, which makes it less of a pain to escape hazards. Another balancing factor is that unlike the official Mega Man games, the bosses don't get ANY Mercy Invincibility.
Kirby Super Star gives most of the bosses this, requiring quick attacks to be done rhythmically rather than simply spammed repeatedly. It also has the unfortunate effect of making Helpers actually detrimental to getting the best Arena time.
Freeware Ninja Senki uses mercy invincibility, but as it comes alongside savage knockback, it's not much of an advantage.
Rayman Origins again makes damage knock you back and you're only invulnerable for about half a second, which is a major factor contributing to the game's Nintendo Hard status.
Iji gives you a few seconds of this whenever you take health damage. Maxing out your strength stat actually increases it. In fact, exploiting Mercy Invincibility is the only way to go through the One-Hit Kill Force Fields surrounding the Null Driver.
On the other hand, one of the bosses has a very powerful attack that bypasses it, to stop some clever players to cheat their way out. The only way to avoid getting hit is stopping the boss from shooting, which has the side-effect of forfeiting an optional upgrade.
Purple makes you invulnerable for a short while when hurt.
In The Smurfs for the SNES, you had mercy invincibility, but so did the only non-bossnote bosses have their own trope enemy that could take several hits: Azrael, who was hard to avoid and naturally, could hurt you while invincible.
And he respawns.
Present in Bug!. Not like it's going to help against swamp water or lava, which will still kill you no matter what.
Sometimes subverted in the first Sonic the Hedgehog, as some objects were exempt from the invincibility, so landing on a large bed of spikes could possibly have you bounce back onto it again, killing you.
Likewise, Sonic Generations will avoid mercy invincibility if you're forced forward and hit spikes, much like getting killed by a crusher trap (thankfully there's only one level where this can happen.)
Soul Blazer had this, as well as one armor that extended its length.
Inverted, but with the same effect, in Super Mario RPG and the Paper Mario series, where contact with an enemy in the overworld would initiate a battle. If you ran from battle, the enemy would flash for a few moments, enabling you to run away without starting a new battle with the same enemy.
In Super Mario RPG, the enemy would function like a solid block for those few moments, allowing you to use them as a stepping stool. This could actually be used at one point in the Kero Sewers to access an otherwise inaccessible shortcut leading to an area near the end of the game, which would allow for some serious Sequence Breaking... except that if you hadn't been on the other side already to knock down a particular barrel off a cliff, it is impossible to scale that cliff from the wrong side... And the game gives you a short message telling you that it's a dead end. The Dev Team Thinks of Everything.
Both played straight and averted in the Mega Man Battle Network series in the case of both the player and bosses. Some attacks triggered mercy invincibility, while others didn't (Usually multi-hitting ones). The latter were initially favored over the former for obvious reasons (Or for those fighting bosses with them, hated), but later games in the series added attacks that ignore and remove mercy invincibility, which made the former more practical to use.
Getting knocked down by enemies in Phantasy Star Online provides with you invincibility that lasts from when you start falling down to a short moment after you stand up, allowing you enough time to use a recovery item to save yourself.
Also present in the sequel, but it's not nearly as helpful as before, as you're now vulnerable the moment you've regained control, meaning you'll just immediately get hit again if an attack is in contact with you when this happens.
Monster Hunter makes you invincible while knocked down, and for a very brief period once you get up; otherwise monsters could just easily bash you to death. Some skills, such as the Felyne Riser skill in Monster Hunter Tri, extend the duration for which you're invincible after you get back up.
In keeping with its Nintendo Hard reputation, Gradius on the NES had a power-up that gave the Vic Viper shields. When the shields took a sufficient amount of damage, they turned red, then another point of damage would make them disappear; however, since the disappearance often came during a flurry of shots and since there was no Mercy Invincibility on the SHIELDS, you could lose the shields with one shot then die the next moment.
Touhou games give you few seconds of invulnerability after dying and respawning, at least in the Windows games. Also, after you finish off one section of a boss's health bar, they often get a couple seconds of invulnerability before you can start draining the next section.
eXceed 3rd Jade Penetrate gives you a few seconds of Mercy Invincibility to give you enough time to fly around the screen to pick up the Mini-Tiamats you dropped on death.
Minimal in The Guardian Legend, providing less than a second of protection, and only against small enemy collisions. Large lasers or enemy attacks do so much damage that sustained contact drains your shield almost instantly.
In Afterburner Climax, your plane would flash and be briefly invincible every time an enemy landed a "shack on the target" (missile hit in non-military lingo), which prevents the already difficult game from becoming even harder given the enemy love for ripple-fire Macross Missile Massacre.
In Mega Man Legends, Mega Man gets a second or two of mercy invincibility each time he gets knocked down. What makes this game notable in this regard is that there is an item (the trademark Mega Man helmet) that makes him much harder to knock down. The game plays this off as a good thing, but if you can't be knocked down, that means many enemies can just keep you in stunlock (i.e. flinching so many times you can't move at all) with machine gun fire until you are dead. Being knocked down causes you no extra damage, and allows you enough time after you get up to move out of the way.
Mass Effect 3 multiplayer has this in the form of the Health and Shield "Gates", when reaching 0% shield or 5% health a short invincibility is activated of a length depending on the difficulty level. To prevent too much abuse it can only be triggered every few seconds.
Not in the main body of Bully, but shows up in the arcade games that are available. Most are needed for 100% Completion, and one ('Consumo') mandatory to unlock a Save Spot. That particular game even lets you trigger it without dying; if you're bounced off the playfield, you're reset in the centre with Mercy Invulnerability.
The Trogdor faux-arcade game on the Homestar Runner site does this when you die and respawn, because the enemy archers and knights don't reset.
The mobile game Clash of Clans has a "Shield" mechanic, which prevents the player's village from being attacked by other players (and is lost if the player decides to attack another player's village) which can be purchased using real money. At the start of the game, each player gets a free shield for two days while they get their village started, and taking enough damage during another player's raid will grant the village a free shield whose duration is based on total damage taken.
To demonstrate the importance of this: there was no temporary invincibility in the Genesis game Toejam And Earl. Any enemy which could move faster than the main characters could walk could hit them over and over without giving them any chance to get away or retaliate. Thus the player could be "juggled" into oblivion by a single wimpy enemy.
You actually could get mercy invincibility in one case: getting flattened by an giant hamster ball, or the ice cream man. However, this only protected you from getting squished again for a few seconds; normal attacks from enemies would still hurt.
In Secret of Mana most enemies in the game, after being hit with a physical attack, would enter a stunned state where further attacks apparently did not affect them. Unfortunately for weaker enemies (and, annoyingly, your characters) attacks that hit while the target was stunned would do damage the moment the stun period ended, immediately leading to another stun period and so on.
Annoyingly subverted in Deadly Towers. All damage you take knocks you backwards and you don't regain control until your Mercy Invincibility wears off (which lasts less than half a second either way), meaning you can't get away from any enemies who may also try to attack you from behind (such as the quick-moving bat enemies).
In a very rare example of this applying to enemies, the tall enemies that throw boulders in the inverted castle's underground cave have the rock included in their hitbox when they hold it, but no invincibility frames. Play as Maria in the PSP remake, shoot a dove at the rock, and they will take damage for every frame the dove touches the boulder.
The Ys series averts this hard, except in later games when you get knocked down. XSEED's trailers for The Oath in Felghana even use this as a selling point!
Averted completely in the Pokémon Rumble series, making it rather important to deal with large groups of enemies cautiously.
Devil May Cry 3 has a notable absence of Mercy Invincibility for normal hits; instead, you get stunned! So you can start at full health, get hit once, and have a mob of enemies finish you off before you're allowed to react. As a small measure of kindness, though, the game allows the third hit in a row to knock you down and away from the mob (assuming you survive it, damn you Dante Must Die!), and you're given Mercy Invincibility at least until you get back on your feet.
inFAMOUS doesn't give Cole any mercy invincibility when he's hurt, but enemies tend to hold their fire for a second if you get knocked down. With some glaring exceptions. The First Sons Conduits are key examples; if you're attacked by multiple ones, the first will knock you down with a shotgun blast, at which point his allies will shoot you while you're down.
Inverted in the SNES port of Captain America and the Avengers where enemies can pummel you down to nothing in a quick succession of blows, but get mercy invincibility as the player hits them, preventing them the chance to do more than small increments of damage at once while staying wide open and vulnerable. Combine this with the fact that the first level took over a minute to start on a black screen (what the hell? A cartridge game with LOAD TIME?) and you begin to understand why nobody ever talks of this game.
The oldie Jet Set Willy did not have mercy invincibility either. While the player can reappear far from the enemy, he can also reappear right on it, and lose all his lives in mere seconds.
Another example of its importance: Joe in the game Viewtiful Joe usually has Mercy Invincibility on taking a hit. However, during the fight with "Another Joe", one of Another Joe's attacks spawns clones that fly around the screen and try to hit you. Joe does not get temporary invincibility if a clone hits him, but he still reacts to the hit, during which time he's frozen — and any other clones may freely hit him. It's quite possible to go from full health to getting killed this way if there are enough active clones.
Another Capcom game, Mega Man Zero 3 the final boss has a sword combo that ignores Mercy Invincibility. Keeping out of range is essential in winning the battle. When said boss appears as a Bonus Boss in Mega Man ZX he has the same combo. Beating him, retrieving an item afterwards, and then beating the game allows you to play as him, with everything EXCEPT the extended sword combo.
The Zero series gives each attack a "priority" that determines what kind of combo it can do. In essence, an attack will ignore mercy invincibility if its priority is higher than that of the attack that caused the invincibility. All attack chains in the game simply have ascending priority; saber combos from Zero and 3's final boss have highest priority.
Spikes in the first version of the original Sonic the Hedgehog would not trigger Mercy Invincibility at all, leading to situations where a player could land on a large area of spikes and lose their shield, rings, then life in one go as Sonic bounced uncontrollably from spike to spike.
SNK's (pre-Neo Geo) game Athena, being a very early platformer, did not feature this trope. Combined with the fact that enemy AI consisted of "follow the player", it only took one misstep to completely deplete your life bar from full.
In PC platformer Elf the player has a health bar that simply decreases gradually as long as you keep touching an enemy - no mercy at all.
The first two Turrican games lack Mercy Invincibility and all enemies from the first mook you see to the final boss deal damage at the same, very fast, rate. Frustration is avoided however as damage does not stun you and so you won't get bounced to death.
Present in The Adventures of Lomax, as long as you're wearing a helmet (your Single-Use Shield). It comes with a certain annoyance: if you get hit, a spare helmet that is placed in a slot at the top of the screen starts falling down; if you can't catch it in time, you are left with none and become a One-Hit-Point Wonder.
Played straight and averted in Shin Megami Tensei III: Nocturne. While a new fight won't start the moment you finish your last fight, it's still entirely possible for a new team of demons to show up as reinforcements in the first fight after you beat the first team. With the skill riberama to make the odds of battle increase you can occasionally fight up to four or five teams in a row.
The Pokémon games just don't have it at all. Say you are facing north and you want to take a step east. It's entirely possible to get one wild encounter when you turn to face east and another one when you move to the tile east of you.
This can be abused in games with the safari park as you can simply spin in place for encounters and not have to waste any steps at all.
Painfully absent in the indie shooting game Sapharica. It has some pretty dense bullet hell. You never get invincibility in the game. Not even when bombing.
In Bangai-O and Bangai-O Spirits, your Humongous Mecha can easily be stun-locked to oblivion by the enemy's Macross Missile Massacre, unless you counter with your own. Good luck when you don't have the super meter to launch your own missiles, though.
The total absence of this in the NES version of Metal Gear is one of the many reasons why that version is reviled by Kojima. Both MSX2 games and even the non-canon NES sequel Snake's Revenge gave players temporary invincibility every time Snake gets hit. This is actually a necessity in Metal Gear 2: Solid Snake, since it makes it very easy to defeat Dr. Pettrovich, who sneaks up behind Snake and tries to strangle him. Because the player constantly receives damage from the choke-hold, Snake is constantly in Mercy Invincibility, meaning it's possible to kill the boss just by firing remote-controlled missiles at his own back. He also had Mercy Invincibility in Metal Gear Solid, but it was excised from the sequels and the remake in the name of realism.
It's also inverted in the Cyborg Ninja fight in Metal Gear Solid. The Ninja starts flickering after three hits, so that the player can't keep spamming attacks (unless the player uses a chaff grenade to disable him beforehand, in which case he starts blinking after only one, for the same reason). Snake, on the other hand, gets no such mercy, and if you don't get up in time, the Ninja will jump into the air and stomp on Snake, dealing massive damage.
A common rule in the children's game of Tag is "no tag-backs", meaning that once a person has been tagged as "It", the person who tagged them must be allowed to get away without being tagged right back.