Nigh Invulnerability/Tabletop Games

Examples of in  include:

Card Games

 * In the Mirrodin block of Magic: The Gathering, there is a substance called darksteel that certain objects, including some artifact creatures, are made of. Anything made of this substance is indestructible, meaning in game terms that it can't be destroyed or killed (although it can be removed through indirect means). A prime example of this is Darksteel Colossus, a huge artificial giant that not only can't be killed by usual means, but if someone manages to actually send it to the graveyard, then it is simply put back into its owner's deck to be drawn again later. The indestructibility mechanic was retained and used in later blocks, and has been applied to many things not made of darksteel.
 * just as an idea of how indestructible it is, Word of God says that it is easier to rewrite the laws of physics such that you find a piece of darksteel in the shape you want than it is to forge the darksteel by any conventional means.
 * Also in the Magic Universe is Squee, an innocent and friendly goblin who just couldn't stay dead. What started out in the books as him simply not retaining any damage as a form of comedic discontinuity was latter changed into a legitimate supernatural ability, causing him to come back from any level of abuse, even death. Unfortunately for Squee,
 * Another MTG example is Lord Konda, the evil daimyo of Kamigawa, who stole a powerful spirit from the otherworld and bound it inside an artifact that granted him eternal life and imperviousness to harm.
 * Possibly the oldest example of this trope in MTG is the "Regenerate" mechanic, which (almost always for a cost, though usually a small one) negates the next attempt to kill or destroy the thing being regenerated, presumably by means of a phenomenal Healing Factor. With the right cards and a healthy stockpile of mana, your entire army can essentially become nigh-invulnerable.
 * There are a handful of creature cards with the "Phoenix" subtype, all of which have some ability that allows them, like their legendary namesake, to come back from the dead. The cost and repeatability of this varies, but rest assured if your opponent puts a Phoenix on the battlefield, you'll probably have to kill it at least twice.
 * Platinum Angel gives you Nigh Invulnerability, stating quite simply that while the angel is in play, you can't lose the game and your opponents can't win the game.
 * If you can get your life total above 30 while he's on the field, Rune-Tail, Kisune Ascendant becomes an enchantment that makes all your creatures impervious to any and all forms of damage.
 * Honestly, there are lots of cards that confer or possess Nigh Invulnerability, far too many to list here. Yes, this is only a small sampling.
 * Can't forget Ulamog, the Infinite Gyre, which at least has the justification of being an Eldritch Abomination.
 * Emrakul, while not actually possessing the "Indestructable" rule, does prevent itself from being countered and being affected by almost all spells (so only colorless artifacts can harm him). Given his insanely high Power and Toughness, as well as the flying ability, this makes him VERY hard to put down.

Roleplaying Games

 * The Tarrasque, a monster from Oral Tradition and added to Dungeons and Dragons, is not only incredibly tough but regenerates at a hideous rate and will not stay dead, and is immunized to 50% of the offensives spells. The only way to kill it is to bring it to -10 hit points (the normal point of death for living creatures in D&D) and cast wish, specifically wishing for the Tarrasque to remain dead.
 * The 4th edition version of the Tarrasque just plain cannot be killed; reducing it to 0 Hit Points simply banishes it back to its resting place at the core of the world. However, while still incredibly tough on account of massive hit points and all-purpose damage resistance, it no longer regenerates.
 * There is a Shout-Out to this creature in Starcraft, in which one of the higher-level Zerg units is called a Torrasque. It is quite durable, regenerates quickly, and is presented as being continually reincarnated by a specific cerebrate.
 * Another Blizzard-related Shout-Out comes from the popular Warcraft 3 map Defense of the Ancients with an item known as the Heart of Tarrasque. Providing a dramatic increase in health total and regeneration, the Hero carrying it becomes difficult to kill except by sustained vicious focus-fire from the enemy team.
 * Anarchy Online also has a Shout-Out to this critter by having it as one of their early endgame bosses, which drop bits of its own body that you can turn into armor.
 * Prior to 3rd edition, lots of D&D monsters had Nigh Invulnerability to weapons below a certain "plus" value, meaning that heroes without such equipment could only defeat them with spells, fire, or improvised alternative methods (e.g. holding a werewolf underwater until it drowns). This rule got the nickname "You Must Be This Tall To Fight This Monster", and was fortunately replaced with damage resistance in 3E.
 * Particularly noteworthy were the AD&D versions of the rakshasa (invulnerable to mundane weapons and nearly all magic) and the intellect devourer (same deal, and even magical weapons' damage would be reduced to almost nothing on a hit).
 * New World of Darkness:
 * While there's not really such a thing as "invulnerability,", Prometheans come pretty damn close. For instance, most mortals and supernatural creatures take wound penalties to all actions after they take a certain amount of damage. Similarly, if their health meters fill with bashing, they have to resist passing out, and if they fill up with lethal, they start bleeding out. Prometheans experience none of this; the only way to put them down is to fill their health meters with aggravated damage. And after that, they can still come back if their Azoth is high enough. Of course, this is the World of Darkness. The only reason they're that tough (gameplay-wise) is because they need to be tough; the world literally hates them, and the only way out is to lose their powers, including invulnerability.
 * Similarly, there are the slashers who follow the Mask Undertaking. Any attack against them, be it with a sword, a machine gun, or a flamethrower, only fills one box on their health meter, and it has to fill all the way before they go down (and even then, that's not much of a guarantee).
 * Old World of Darkness:
 * Mummies are effectivly indistructable. They take damage pretty much the same as any other player character; the difference is they regenerate damage, and have something like 7 wound levels past incapacitated that define various levels of dismemberment to their corpse. The reason? To figure out how long it will take before they can get back up again. The answer is usually, not long.
 * Mages in Mage: The Ascension could take the 'Immunity' Merit, which could be taken to a level to prevent all damage from all save a progressively rarer source. If taken to a high enough level, this could prevent all damage not from such sources as the Public Domain Artifact of choice or more common sources under more stringent conditions (the book itself lists 'mistletoe dagger wielded by a red-headed woman on the night of the full moon' as a viable option). Unsurprisingly, many Storytellers do not allow it in their games.
 * The Vampires in Vampire: The Masquerade had the Fortitude discipline, which was pretty much this trope when you got it past even mediocre levels. If you had enough you could reduce sun and fire from One-Hit Kill to "meh", meaning you could walk around in broad daylight, for a short time.
 * GURPS has the Supernatural Durability advantage that gives the ability to survive any amount of punishment unfazed until you reach -5xhp and even then only one form of damage can truly kill you. The rules do say that being blown to pieces by a single attack is still lethal.
 * In GURPS: Supers on the discussion of cosmic scale characters buying enough Damage Reduction to divide an attack's damage by one billion is noted as being "alarmingly cheap" at just 1350 points. Consider that the destruction of Hiroshima required not even a hundred thousand points of damage.
 * Several characters in Scion come with Invulnerability, though this almost always has one caveat - a character with higher Legend can damage them. There are some exceptions to even this, however.
 * Liches in most games that have them will regenerate from any sort of destruction unless their Soul Jar is broken first.
 * In Nobilis, all Nobles know a simple rite that renders them immune to a certain level of mortal harm. Unusually, as the character gets more powerful, the rite will start to include less severe damage. So, a weak Noble will walk out of a (mundane) nuclear explosion unharmed, but be completely vulnerable to bullets. True masters of this rite can't even be insulted by mortals.

Wargames

 * Not only are Warhammer 40000's Necrons Terminator-like metal skeletons with amazing damage resistance, they have the ability to teleport matter directly to their own system from their tombs for nanites to incorporate it into their forms as a self-repair mechanism powerful enough to rebuild them even if cut to pieces. And if you DO manage to get one to stay down, its various component parts will be teleported back to the tomb and rebuilt no matter what sort of damage has occurred. The Imperium doesn't even know if there exists weapons that can kill Necrons. And given the kind of weapons that exist in Warhammer 40000, that's saying quite a lot.
 * One Necron managed to directly regenerate from being melted into a puddle of metal. And this was not even a leader, just a Necron mook.
 * There is technically a way to kill Necrons and possibly their C'Tan gods—hitting them with weapons that expose them directly to the Warp, since their existence is purely material, and they can't survive the Immaterium. That's the purpose of the Blackstone Fortresses aka Talismans of Vaul. The background tends to get retconned with every version release, so this may no longer be valid.
 * Daemons aren't so easy to dispose of either. Powerful ones cannot actually be killed (at least with physical weapons), merely banished back into the Warp, and even doing stupendous amounts of damage only make the banishment longer. Kill a daemon, and he'll probably be back in a couple centuries, which isn't much time in Warhammer 40000. Other supernatural entities share similar traits, such as the bodiless "walking armor" soldiers of the Thousand Sons legion of Chaos Space Marines, who have an annoying tendency to come back from the dead.
 * Space Marines almost constantly wear armour better than most tanks, underneath which is a three-metre-tall Super Soldier with a bullet-proof chest and multiple spare organs. Even severe damage near to the point of death doesn't stop them, as they are wired into a Dreadnought and continue fighting.
 * Da Orks are already ridiculously tough, being hulking brutes with physical strength equal to or greater than a fully equipped Space Marine, but they are further resilient due to being animals with a symbiotic relationship to fungi, almost completely devoid of vital organs and any injury short of missing limbs being superficial (it is thought that bolters, self-propelled explosive rounds, were invented originally to combat Orks). There are reports of Orks being decapitated, killing the person who decapitated them then reattaching their own severed head, with no problems whatsoever. Datz reel Orky.
 * Makari (Ghazghkull's standard bearer) had the supernatural luck version of this, effectively granting him a great saving throw against pretty much anything. The most recent codex informs us that he "lived to the ripe old age of nine before finally being sat on by his master and subsequently fed to an ill-tempered Squiggoth."
 * The dwarves from the Warhammer Fantasy Battle games. While still being mortal and technically still squishy on the inside (so no "Made of" rules) the Blood Bowl rule book comments on their "Stubborn Knack of refusing to Die".