Always-Accurate Attack

Any attack with an absolute, guaranteed 100% chance-to-hit when used in battle (or alternatively, any technique/skill that grants this status to another attack). This can be a valuable tool against certain targets who are otherwise difficult to actually land a strike against (due to speed or size), but will usually involve a tradeoff of lower-than-average damage output compared to other attacks.

Note that the fact that this attack will always hit the target doesn't mean it will necessarily damage it -- in fact, this is a chief balance issue in Video Games, where an Always Accurate Attack almost never overlaps with Armor-Piercing Attack or Unblockable Attacks (to prevent the attack from becoming a Game Breaker). Also note that even an Always Accurate Attack can be forced to miss the target if a Story Overwrite (such as Cutscene Power to the Max, or a Hopeless Boss Fight) is in effect.

See also Improbable Aiming Skills and No Saving Throw. May be Boring but Practical due to its reliability that it will hit the target.

Anime and Manga

 * Yu Yu Hakusho: Kaname Hagiri, codenamed "Sniper", whose territory allows him to throw any object to hit its mark with lethal force.
 * Vander Decken in One Piece has the devil fruit ability to "mark" a person he's touched so that any object he throws, it will always propel itself to hit the mark, the thrown objects will follow its mark indefinitely until it hits something, however he can only have two people marked at the same time (one for each hand).
 * Fiamma of the Right from To Aru Majutsu no Index has "The strike that reaches everything when swung". It reaches the target without any speed, meaning it cannot be dodged.

Card Games

 * In Lunch Money you can "grab" someone, which by itself does nothing. If they play an "avoid" card, they get out of it, but if they don't have it (or for whatever other reason decide not to play that) your next attack is unblockable.

Comic Books

 * One of the stated properties of Darkseid's Omega Beams is that they track their targets unerringly across space and time, and always eventually hit what Darkseid intends to hit. Except when they don't.
 * The Saint of Killers in Preacher (Comic Book) wields supernatural six-guns that never miss and always inflict a lethal wound. They were forged from the sword of the Angel of Death, explaining their unusual properties.

Film

 * Parodied in Grindhouse Planet Terror; the hero guy never misses. As he lies dying, his girl is sobbing over him begging him not to leave her alone. He pats her belly and says she won't be; he never misses.
 * The unnamed protagonist in Hero had an attack that could not miss its mark if he was within ten paces.
 * Zorg demonstrated a variant in The Fifth Element with his special ZF-1 gun: After shooting a target once, a "replay" feature can cause every subsequent bullet to strike the same target, regardless of the direction in which it was fired.
 * The Huntsman in The Tenth Kingdom has a crossbow that, when fired, will always pierce someone's heart. The queen gave it to him in a deal--all he had to do was close his eyes, turn around a few times, and fire once at random. (He killed his own son from several miles away.)

Literature

 * In Fred Saberhagen's Book of Swords series, this is Farslayer's stated ability: Throw the sword with a target in mind and Farslayer will fly unerringly towards that target, no matter how far away, and strike him down. The drawback to this is that it's a one-way trip, leaving Farslayer there for anyone to pick up and use.
 * The Arabian Nights/D&D-style fantasy novel Red Sands uses this with a twist when the protagonists acquire a magical bow from an efreeti. Arrows fired from the bow will "never miss and always slay"...somebody they're not pointed at, as it turns out. This quirk actually saves one of the heroes who happens to accidentally be right in the line of fire when one arrow is loosened, and is put to creative and this time deliberate good use in the climactic last fight scene of the story.

Mythology

 * Older Than Print: This ability is one of the properties of the Norse god Odin's spear Gungnir.

Tabletop Games

 * Dungeons and Dragons
 * 1st Edition Deities and Demigods Cyclopedia.
 * Celtic Mythos: Goibhnie, the god of blacksmithing, makes weapons that never miss. Morrigan has two spears that never miss.
 * Central American mythos. The god Xochipilli's attacks don't miss.
 * Chinese mythos. The goddess Tou Mu has a bow that never misses an opponent within 100 yards.
 * Egyptian mythos. The god Apshai's bite never misses. Bes, the god of luck, never misses with his attacks.
 * Greek mythos. The goddess Aphrodite can damage opponents just by waving her hand. The goddess Athena never misses her targets. While the goddess Tyche is looking at a creature with only her right eye, the creature will always hit any target it attacks.
 * Hindu mythos. The goddess Ratri can give an angry look that does damage automatically. The god Tvashtri has a device that fires beams that always hit their targets up to 300 yards away.
 * Melnibonean mythos: Arrows of Law will always hit a chaotic creature. The demigod Haaashastaak always hits with his bite.
 * Nonhuman deities. Corellon Larethian has a bow that never misses.
 * Norse mythos. The god Forseti's sword always hits any opponent who has lied in the last 7 days or is chaotic. Thor's hammer Mjolnir never misses when thrown. When firing his bow the god Uller's bow never misses targets less than 200 yards away.
 * Sumerian mythos. The goddess Inanna can aid warriors by making sure they never miss an attempted hit.
 * 3.X Edition Deities and Demigods: greater deities are treated as always rolling the maximum possible value on attack rolls: i.e. natural twenties every time. In D&D, if you get a natural twenty on an attack roll, you automatically hit, regardless of what your total attack roll actually is. In other words: greater deities always hit. Now throw in the fact that the "maximum roll" rule also applies to damage rolls...
 * Some spells simply always hit (Magic Missile is the poster child for this in all editions including the 4th post-errata), and many others will still have at least a reduced effect on the target even on a nominal miss (successful saving throw in 3.x and earlier).
 * Flamethrowers in Warhammer 40000: Everything under the template automatically takes a hit, the template doesn't scatter (unlike blast templates used for explosive shells) and no cover save is allowed.
 * In Warhammer Fantasy Battle, the Blade of Darting Steel causes all attacks made with it to hit automatically. Of course, this is not the same as every attack wounding or penetrating the enemy's armor or magical defenses.
 * Possible but very expensive in GURPS. "No Roll Required" causes the attack succeeds automatically (so long as doing so is logically possible) and "No Active Defense" causes any success to hit automatically. With "Ignores DR" you can just erase the targets HP.

Video Games

 * Believe it or not, this isn't limited to RPGs. Some head-to-head fighting games like Backyard Wrestling feature this thanks to shoddy programming that makes projectiles impossible to dodge; they will actively steer themselves in midair toward characters.
 * Smackdown vs. Raw 2008 did something very similar: Dirty wrestlers have the ability to shove the referee into their opponent, and while it is possible to dodge this, the ref will indeed run in the same direction as the opponent, as though he wants to smack into them.
 * Pokémon: Moves such as "Swift" always strike the target, although they can also be negated by Elemental Rock-Paper-Scissors or the moves Protect and Detect. Since the second generation, attacks that involve moving out of range before striking (Fly, Dig, etc.) can also be used to avoid these attacks.
 * "Lock-On" and "Mind Reader" ensure the next attack will hit, even if the target uses Fly or Dig, though the target can still defend itself.
 * The move "Vital Throw" is always accurate with the trade-off of having decreased priority, executing slower than the opponent.
 * The "No Guard" ability grants this status to any move its user performs ... and any move that gets used against them.
 * Fire Emblem the Sacred Stones: the Sniper class has the Sure Strike skill, which ensures a 100% accurate hit if it activates. Unfortunately, this skill tends to be unneeded, as your Sniper characters would have high hit chance anyways, and even worse if it activates when an enemy Sniper attacks your characters.
 * In some Final Fantasy games, magic would always be successful on targets with "Invisible" status -- even Useless Useful Spells. For Final Fantasy VI in particular, even Contractual Boss Immunity could not protect against this, making it a Game Breaker of a Good Bad Bug.
 * Rosa in Final Fantasy IV had Aim, which makes her bow and arrow attacks always hit. This was also carried into the fifth one, and could be used with any weapon.
 * On the subject of 5, the Rapid Fire command. It's 4 attacks per weapon on random targets for half damage, and it ignores the target's defense. The ranger class gives aim and rapid fire at different class levels.
 * In Final Fantasy VIII, the gunblade used by the hero Squall Leonhart has maximum (255%) accuracy even for its most basic model. This means that Squall never misses with it, even while affected by the Blind status effect. Selphie's final weapon upgrade also gains this property.
 * Final Fantasy Tactics: the "Concentrate" support ability ensures 100% accuracy for all attacks (including magic). If an enemy is asleep, petrified, or stopped, all attacks made against it have 100% hit rate (as the enemy can't dodge). And in one of the game's less fair moments, a pair of assassins have entirely unique instant kill moves with 100% accuracy and a long-ranged Stop move with 100% accuracy. During an escort mission.
 * Final Fantasy Tactics Advance: Featherblow and Take Aim are skills that do half the damage of a normal attack, but with 100% accuracy. It also has concentrate, a passive ability that removes enemy evasion, which can boost instant kill abilities. The result is exactly what it sounds like.
 * Final Fantasy Tactics A2, however, nerfed Concentrate so much it's entirely useless (A mere 5% boost? Compared to 30% or so?)
 * In Last Scenario, attack spells cannot miss, but can't hit critically either. As well, there is the late-game spellcard "Slap". It executes a physical attack which cannot miss and always deals 1 damage [overlap with Fixed Damage Attack].
 * The default magical attack with mage staves in Dragon Age: Origins always hits the target, regardless of the defenses. The defenses do, however, affect how much damage is soaked. And the staves cannot score critical hits.
 * In Breath of Fire IV, Scias's "Shining Blade" is a critical hit that never misses (but can be parried), while the "Target" skill is a half-powered strike that cannot be parried (or miss).
 * In some RPG settings, magic ignores accuracy/evade calculations altogether, thus spells will always hit the target.
 * In Runescape, Korasi's Sword and the Dark Bow have special attacks that always hit.
 * Super Robot Wars: the "Strike" buff ensures 100% accuracy for the unit that uses it for the next attack or the rest of the turn, depending on the game. "Attune" does the same thing except one unit casts it on another. Though "Alert" can allow you to dodge anyway.
 * In many Roguelikes, beam-like attacks will hit everything in their path, which often includes things like dragons breathing fire and poisonous gas.
 * In World of Warcraft, the Glyph of Divine Accuracy increases the chance to hit with Smite by 18%, high enough for it to always hit under normal circumstances. Discipline priests attack with Smite to grant themselves the Evangelism and Archangel bonuses and Smiting an enemy will heal an ally for the same amount, but they can still be primary healers. Consequently they don't care about hitting with any other spell, and don't want to waste a lot of gear on improving their hit rating for one spell.
 * One of the SOS Cards in Toontown Online will make all of the other gags used in the same round as it hit. There's also an inversion, another SOS card which causes all of the Cogs' attacks for that round to miss.
 * Battle for Wesnoth has attacks with the Marksmanship or Magical properties. Such attacks will always have a certain accuracy rating no matter what the target's evasion value is. Very useful for enemies entrenched in terrain favorable to them (like Elves in forest tiles).
 * In Thunder Force V and VI, there is the Free Range. What it does is that it makes a green, wireframe conical shaped area from the character (that can be aimed), and if anything steps into the green area, they are fried by an instant-hit laser that never misses. (Even better if your have three Attack Drones active, as all three will fire too).
 * Sonic's homing attack that he has had in all of the 3D games and some of the more recent 2D games.
 * Rock Man 4 Minus Infinity has the Wish Star Adapter. The attack involves Mega Man and Rush attacking various parts of the screen in a lightning-fast pace. The downsides are the low damage and that Mega Man can only use it once.
 * Disgaea 2: Cursed Memories turned this trope into a character class, the Rifle Demon, commonly called the Baciel. Their attacks always hit, even against characters with high speed or critical HP Ninja (who get insane dodge rates when under 25% HP). Disgaea 3 Absence of Justice possibly broke this wide open by turning this trope into an equippable item, the Naive Glasses (due to the fixed "Heat Seeker" specialist inside of it).
 * Soul Nomad and The World Eaters had this as a room, but, like the Pokemon example up top, it came with the massive drawback of being unable to dodge enemy attacks.
 * While virtually all spells in Kingdom of Loathing are guaranteed to hit, regular attacks and skills which amplify attacks can miss if the enemy has enough defence. The exceptions to this rule are the skill Shieldbutt, which makes your attack unblockable and Lunging Thrust-Smack which will always hit if a 2-handed club is equipped.
 * In the classic Doom series, the Arch-Vile's flame attack will always hit you if it mantains line of sight to you for the duration of the attack sequence. You can only avoid it by breaking line of sight before the explosion with you in the middle of it or killing the Arch-Vile first.
 * Heavy Weapon has your Nukes, which hit everything on the screen. However the enemy also has one: Atomic Bombers drop A-bombs that, if not destroyed before they hit the ground, are a One-Hit Kill on you regardless of where you are on the screen!
 * For a game that heavily relies on countering enemy attacks and avoiding damage, there is a boss in Mario & Luigi: Bowser's Inside Story that uses one. It's even called "Unavoidable attack", and Bowser will take damage from this one no matter what.
 * Gae Bolg in Fate Stay Night has the ability to always pierce the heart of the enemy. "Always" meaning the result (heart pierced) is already set and the cause is created after that, even if it has to involve reality warping. It has the caveat that really lucky people can Screw Destiny and get away with merely getting hit somewhere non-fatally, which conveniently includes everyone the weapon is ever used against.
 * The thrown version, meanwhile, is more powerful but also lacks the reversed cause and effect: It cannot be dodged because it's a seeking missile, but it can be blocked.
 * Tales of the Abyss features "Mystic Cage", Jade's first Mystic Arte. All enemies, regardless of their position on the battlefield, is encased in a sphere of pure magical energy, which explodes and damages all of them.
 * On a general note, the Mystic Artes throughout the Tales (series) are with few exceptions, guaranteed to at least connect with the enemy that's the user's current target. Also, some spells strike the entire battlefield and/or freeze the action when they go off, which makes avoiding damage from them impossible outside of using invincibility or being immune to their element.