Invincible Mario

Invincible Mario is a form that makes its debut in Super Mario Bros. Mario can assume the form after using a Super Star, which made its debut in the same game; while in this state, he is unaffected by both enemies and obstacles, and can defeat most of them by simply touching them. However, the state only lasts a few seconds, and Mario can still lose lives from falling into a pit, touching lava or poison water, being crushed, touching Volcanic Smoke, getting crushed between a wall and a Boohemoth, or running out of time. Invincibility is usually depicted by a flashing, color-changing character. Unless he's already in another invincibility-granting form (like the Mega, White Raccoon, or White Tanooki forms, which are incompatible with this form), Mario usually retains his current form while invincible (for example, if Fire Mario gets a Super Star, he becomes invincible, but retains his Fire form).

In most games, when Mario is damaged, he will be invulnerable for a few seconds as well (though he cannot defeat enemies).

Super Mario Bros.
Super Mario Bros. marks this form's debut. Enemies defeated by this form will give the same points as if they were beaten normally.

Super Mario Bros. 2
In Super Mario Bros. 2, Super Stars, and thus invincibility, are gained by grabbing five Cherries. Because enemies respawn off-screen and hearts spawn for every eight foes defeated (except in Super Mario Advance, where a traditional Super Mario World-style point system is added), this form is mainly used to recover health.

Super Mario Bros. 3
As of Super Mario Bros. 3, Mario flips when he jumps in this form, in a similar fashion to Samus Aran. Also, there are some ? Blocks that normally contain coins, but will contain Super Stars if Mario or Luigi is invincible when they strike the block. This allows the player to string together a long period of invincibility, and thus gain even more points (and in Super Mario Advance 4: Super Mario Bros. 3, extra lives).

Super Mario World
Starting with Super Mario World, Invincible Mario starts earning extra lives from the eighth enemy defeated onwards (which also gives an increasing point reward up to that point). This property was also included in the Game Boy Advance remakes of Super Mario Bros. 2 and Super Mario Bros. 3, which originally did not have it.

Super Mario 64
While Invincible Mario doesn't return in Super Mario 64, the Metal form has a similar function, destroying any enemies Mario touches.

New Super Mario Bros. series
In the New Super Mario Bros. series, Invincible Mario returns, working as it used to. In addition to making players invincible, it also increases one's running speed in New Super Mario Bros., and it can be shared in New Super Mario Bros. Wii, New Super Mario Bros. U, and New Super Luigi U if an invincible player lifts a vulnerable partner (or vice-versa). The latter three games also give Mario the ability to defeat Enemy Courses on the map without entering them, though he won't get any items from them.

New Super Mario Bros. also features Mega Mario, which is similarly invincible.

New Super Mario Bros. 2, in addition to bringing back the Mega form, also introduces White Raccoon Mario (gained just like the White Tanooki form from Super Mario 3D Land), which gives permanent invincibility for the level in addition to Raccoon Mario's abilities, the ability to walk on water (like Mini Mario), and a faster-charging Power Meter.

Super Mario Galaxy / Super Mario Galaxy 2
In Super Mario Galaxy and Super Mario Galaxy 2, there is a similar form known as Rainbow Mario that can be obtained by using a Rainbow Star. Unlike the Invincible form, the Rainbow form speeds up until it expires and can break through objects, but it cannot give Mario extra lives, nor can it be combined with any other form.

Super Mario 3D Land
In Super Mario 3D Land, Invincible Mario makes its 3D Super Mario debut. As in Super Mario Land 2, Mario must only defeat five enemies to start gaining extra lives, rather than the usual eight. Unlike in most games, Mario merely glows golden while invincible in this game.

Also, White Tanooki Mario debuts in this game, becoming available by an Invincibility Leaf after dying five times in a row on a (skipped) normal world course. In addition to Tanooki Mario's abilities, it makes Mario permanently invincible for the level.

Super Mario 3D World
In Super Mario 3D World, invincibility works as it did in the New Super Mario Bros. games, with the only differences being that an extra life is gained for every eighth enemy defeated (instead of every enemy from the eighth onwards), and invincible players merely need to touch others to share the invincibility, rather than grab them. The new Lucky Bell lets Mario turn into an invincible lucky cat statue for a brief time. The Mega and White Tanooki forms also return.

Super Mario Run
In Super Mario Run, the Super Star once again grants invincibility. It also makes characters run faster, activates Coin Rush mode in Toad Rally, and attracts nearby coins (except Black Coins) to the player.

Super Mario Land
Super Mario Land features the same invincibility as in Super Mario Bros.

Super Mario Land 2: Six Golden Coins
In Super Mario Land 2: Six Golden Coins, Mario starts earning extra lives from the fifth enemy defeated onwards, rather than the eighth.

Mario Kart series
In the Mario Kart series, every driver can become invincible by touching and/or using a Super Star, allowing them to drive faster and make other drivers spin-out or tumble by touching them, unless both drivers are invincible, in which they bump each other normally. The Super Thwomps of the original Rainbow Road are also invincible, causing the same effects to any driver that runs into them.

Appearances in other games
In Wario Land: Super Mario Land 3, Wario can use Super Stars to gain this form; he becomes much faster and gains 10 hearts for each enemy destroyed by touch in this state.

In Donkey Kong Country 2: Diddy's Kong Quest, Donkey Kong Country 3: Dixie Kong's Double Trouble!, & Donkey Kong Land 2, the Kongs can become invincible by breaking through an Invincibility Barrel. While invincible, they gain the same effects as a Super Star, such as flashing and defeating enemies with a mere touch. They also still lose a life if they fall in a pit, even when invincible.

In Mario & Luigi: Bowser's Inside Story, in one of Bowser Memory M's moves, he uses a Super Star to become invincible and attack the Mario Bros., complete with the theme music and the effect of knocking a hit bro off-screen for the move's duration.

Invincible Mario makes a small appearance in Mario Golf: World Tour and  Mario Sports Superstars as a post-hole animation, specifically when either Mario or Gold Mario/Metal Mario receives an Eagle or better.

In Yoshi's Woolly World, once Yoshi touches an Invincibility Egg (which spawns after five deaths), he will glow orange and be immune to damage from enemies and their attacks. However, Yoshi cannot instantly defeat enemies by touching them, and he can still be pushed by enemies, and instantly defeated by spike pits, bottomless pits, lava, and being crushed.

In Mario sports titles where Super Stars appear as items, invincible characters will become immune to the effects of other items.

Appearances in other media
In The Super Mario Bros. Super Show!, neither Invincible Mario or Luigi ever made an appearance, as a Starman would not turn Mario or Luigi invincible, but instead served as an alternative to the Fire Flower for becoming "Super Mario" or "Super Luigi". In The Adventures of Super Mario Bros. 3 and Super Mario World, Starmen functioned as they normally did in the games, granting them their Invincible forms for a limited time.

Trivia

 * Invincible Mario's theme in New Super Mario Bros. is reused from the theme of Wing Mario/Vanish Mario from Super Mario 64, which in turn is an arrangement of Superstar Mario's theme from Super Mario World 2: Yoshi's Island.
 * A slowed-down remix of Invincible Mario's theme plays on Star World from Super Mario World.

Reference
Unverwundbar-Verwandlung Mario Invincibile