No Saving Throw

Hey, that guy is going to Mind Control you or try to fool you with an illusion! Maybe, if you focus and struggle against his power, you can -- !

Nope.

Normally in fiction, powers have some chance of failure, whether through lack of skill, Heroic Willpower on the part of the would-be victim, or some other factor that does not make the power 100% effective. But some powers are such that they work automatically if they hit, regardless of any special defenses, resistances, or countermeasures the person on the receiving end may have. You can't see through the illusion, you can't cure the poison, you can't resist the mind control, people hit by the Disintegrator Ray die instantly 100% of the time no matter how important they are.

The Trope Namer here is Dungeons & Dragons, where normally, harmful effects such as mind-controlling magic, dragon breath, illusions, or other supernatural nastiness allows the character affected to make a saving throw of the dice to negate or minimize the effect. Some spells and effects, unfortunately, such as the Level Drain ability of a wraith, do NOT allow a saving throw to be made against them. In more modern editions of the game, these effects almost always have a chance to miss instead.

Contrast Always Accurate Attack. Complete opposite of Won't Work On Me. May overlap with Evil Is Not a Toy. See also Unblockable Attack. Compelling Voice is a Sub-Trope of this. As would Gameplay and Story Segregation in certain cases.

Do not confuse with Author's Saving Throw.

Anime and Manga

 * Geasses in general work like this in Code Geass. The only thing that even has a chance of countering one is another Geass, but that's more of a case of bypassing some aspect of their Geass, like a telepath not being able to read something that the target doesn't know about, or thinking that something is true because their target believes it is.
 * There are two exceptions to this: In the first season, manages to resist for a moment, which Lelouch later deduces was because the command was just so completely against every facet of her character. In the second,  also manages to break out of a geass;, but that took years.
 * There's also that it may be that and that his ability is not blindness, with that particular one being a side-effect of some sort and said character's never being said to recover from the actual affliction.
 * Happens in Dragon Ball GT during the Super #17 arc. Regular #17 is being mind controlled by a second version of himself, and attacks #18, his sister. Krillin tries to bring him out, and he nearly goes back to normal before the other #17 enters his mind again and makes him shake off the good influence, at which point he kills Krillin instead.
 * This is the reason Aizen's Zanpukutou in Bleach is considered overpowered. If you've seen his sword, he's hypnotized you and can control all your senses as he pleases. It's essentially permanent, undetectable, and it's not even the final form of his sword.
 * Tsukishima from the Full Bring Arc has a similarly broken power, he inserts himself into the past of anything he cuts. For a person, this could mean anything from, "Tsukishima is my best friend forever and I don't want to fight him," to "Tsukishima has known me for a long time, therefore he knows all my powers and weaknesses." All it takes is a nick, and it's in effect.
 * It still fails against Byakyua because the latter considers his honour-debt to Ichigo (which Tsukishima can't affect directly) more important than anything else. He therefore kills Tsukishima while acknowledging that he was the most important person in his life.

Literature

 * In the first book of The Dresden Files, nothing can protect you from the Big Bad's heart-ripping spell. Except, of course, striking first.
 * The RPG rulebook clarifies that this is the result of the absurd amount of power in the spell, measured in shifts of power. A typical "attack" spell used in combat can have between 3-10, which can kill, but the target has the chance to mitigate it or negate it via his defensive roll and taking consequences instead. The heart-exploding spell generated over 35 shifts, which is enough to simply overwhelm each and every way a character can mitigate damage.
 * The rules for a lethal Entropy Curse are similar, in that to avoid it, you'd have to roll somewhere in the mid 20s to dodge the "attack," with a skill that likely maxes out at 5, and dice that on their best roll will only add a +4.
 * All that said, the RPG book is explicit and insistent in averting this trope inasmuch as you always get a defense roll. Some tactics might effectively reduce or augment the defense roll, and in situations such as the Entropy curse a defense roll might, in fact, be meaningless, but you always get the chance to defend.
 * Most spells in the Harry Potter series seem to work this way; the Imperius curse is a notable exception that a strong-willed person can shrug off, as Harry learns to do.
 * There is also a basic spell that can protect from some others, but notably not from the Killing Curse.
 * Really, nothing can. Except for love. Or a physical object.
 * In The Wheel of Time, balefire is this. Anything it hits- whether that be a physical object, a person, a city- will be instantly and irrevocably erased from existence. The only way to survive is to dodge it or kill the person making it before they let loose.
 * In Xanth, this trope is the reason the Magician Trent is considered so dangerous before his Heel Face Turn. His Baleful Polymorph powers work on everyone, period. When he tries to use them against Bink, who has permanent Anti-Magic, the only possible counters the antimagic can create are for Trent to miss, or to hit something else. The transformation magic is that powerful, there's no defense against actually getting hit.

Live Action Television

 * In the Power Rangers Turbo movie, when Kimberly and Jason were Brainwashed and Crazy they tried The Power of Friendship which had a very minimal effect, and the only solution was some magic from the local wizard.
 * Picard in "The Best of Both Worlds" told the Borg hive he would fight them with all his strength. The Borg replied "Strength is irrelevant." In the follow-up episode after the two-parter, Picard tearfully confessed that he was completely helpless.

Visual Novel

 * If someone bearing the Mystic Eyes of Death Perception hits you in your point of death, you die. Doesn't matter if you can reincarnate, you are a gestalt entity of six-hundred sixty six different beasts that ordinarily have to all be killed at the same moment, you can locally reverse time to instantly repair any damage done to you, or the world itself actively works to sustain your continued existence, you die. Period.
 * Unless, of course, you have the right flavor of Plot Armor. Arcueid and Souren Araya both manage to overcome this in different ways (the latter by meditatively delaying his death for a considerable time, and the former by simply not having a point of death at night).

Tabletop RPG

 * Call of Cthulhu (tabletop game) loves this trope.
 * Warhammer 40,000 has many weapons that bypass Armor Saves and a few ones that bypass Invulnerable Saves. The wording on one of these attacks simply states that the affected model is "removed from play with no saves of any kind allowed".
 * A favourite tactic of Chaos players in the days of 3.5 Edition was to create one of these by taking a Chaos Lord with the "Daemonic Stature" daemonic gift and the "Dreadaxe" daemonic weapon. Hilarity ensued, then nerfing.
 * Warhammer Fantasy Battle tends not to have outright remove-from-play spells, instead using spells that require rolls against characteristics not typically used for resisting damage; of these the much-maligned Purple Sun of Xereus is probably the most famous.
 * If you are level 4 or below in Rules Cyclopedia Dungeons & Dragons, if someone casts a Sleep spell upon you, you're as good as sleeping, as it doesn't give you a saving throw against it. If you don't have any friends to protect you or wake you up when you're under the spell's influence, you're pretty much at the mercy of whoever cast the spell on you, as anyone can use a bladed weapon to kill you instantly no matter how many HP you have.
 * As mentioned above, the Level Drain attacks of many undead do not allow a saving throw, except for special circumstances.
 * Do not look at a Catoblepas straight in the eyes unless you want to die.
 * Do not touch a Sphere of Annihilation unless you want to be blasted out of existence. Notably, an upgraded and sentient version (the Blackball) released to fight characters of level 38+ (out of a possible 20) was still less scary, since it allowed an (admittedly, very difficult) save.
 * In the 1st edition, a Nightcrawler's sting attack has a 1 in 8 chance of killing a character outright, without a saving throw.
 * the only defense against Holyword and its sister spells (dictum, word of chaos, and blaspheme) are being a high enough level, spell resistance (which is not the same as a saving throw), and having the right alignment.
 * Mutants and Masterminds second edition has No Saving Throw as a extra you can apply to one of your powers. When the power resolves, the target is treated as though they failed their saving throw by one point. For damage effects this results only in Scratch Damage. But for Save-Or-Lose effects like Mind Control, Transform, or Power Control, this ability becomes a Game Breaker. It's typically reserved for NPC Villains.
 * A different example from the same game is the Perception range commonly seen on mental powers. While not a literal example (as the target is still allowed a Saving Throw), it automatically hits any target the user can perceive. A Perception Range power with the No Saving Throw modifier is unavoidable and irresistible unless you can find some way to avoid being seen.

Other

 * In Gamers 2: Dorkness Rising, there's another literal example. Two PC's encounter a death demon, and his compelling fear aura is so powerful they can't roll high enough to resist so the DM assumed that they were compelled. However, the Rules Lawyer says that on a 20 any action is an automatic success, and insists on rolling... a 1. He becomes completely compelled.
 * The most basic magical attacks from the wizard's staves in Dragon Age: Origins can't be run away from, regardless of the target's defences. On the downside, their damage is not that high, and it's impossible to land a Critical Hit with a staff.