Invincibility (無敵 Muteki?), also called Invincible, Invinsible Protect and Invincible Barrier, is a general power-up in the Sonic the Hedgehog series which can be found in Item boxes marked with either a four-pointed stars or colorful sparkling shield. When the player obtains this power-up, the playable become immune to most damage-causing hazards for a short period of time. The player also has different sparkling effects around the playable character, while using the Invincibility.
The Invincibility first appeared in the original 16-bit version of Sonic the Hedgehog and has since become a recurring power-up in the series. The effects of Invincibility has been mostly untouched, like Super Rings, Power Sneakers and other Item Box power-ups, but in several games, it has possessed other different features. While Invincibility has not been as generally featured as it was in the earlier games, it is occasionally used in the latest games as well.
Since from earlier games, when the player obtains Invincibility power-up, the playable character can destroy enemies upon physical contact and cannot take damage from enemies or obstacles, though the player can still lose a life when being crushed under objects, drowning underwater, falling into a bottomless pit or if the timer exceeds 10:00 minutes. The duration of the Invincibility usually lasts about 15–20 seconds before it fades out, though the length of the Invincibility can differ between certain games. After the time runs out, the Invincibility will disappear and the player becomes vulnerable to enemies and obstacles once more.
When using Invincibility, the playable character is surrounded by a bright aura, which are able to metaphorically show when Invincibility is in effect. The visual aura effects from Invincibility differs somewhat between the games; when using Invincibility in the earlier games, the player is surrounded by a field of countless sparkling stars, while since Sonic Adventure, effects are seen featuring more colorful sparkling around the player. In Sonic Heroes, the effects around the player are glowing lines. Whilst Invincibility is in effect, the background music of the Zone changes to a more dynamic-sounding theme, which is usually either a rendition of the game's main theme, or another theme exclusive to Invincibility.
Mostly in spin-off games, Invincibility can function and appear slightly differently from how they are presented in the main game series. In Sonic Drift and Sonic Drift 2, Invincibility is featured as one of items in the game, which can be found in blue monitors called Blue Monitors (無敵BOX Muteki Bokkusu?, lit. "Invincible Box"). When activated (in Sonic Drift 2 the player has to activate it manually), it makes the player invulnerable to obstacles on the tracks, while a familiar tune can be heard in the background. In Sonic Labyrinth, there are featured odd, flashing objects that change their coloring and line formation all the time. If the player touches it and gets red formation called Twinkle (トゥインクル Tuinkuru?), it gives Invincibility to Sonic. In Tails' Skypatrol, Invincibility is a small orange stake with a star, standing on the ground, which Tails can pick up with the Ring.
Since Sonic Unleashed, Invincibility, along with other Item Boxes, has become almost completely absent. When Sonic is using the Boost, it makes him temporary invincible against enemies, but it does not protect him from hazardous obstacles. In the Nintendo DS version of Sonic Colors, Invincibility was once again featured, this time as Item Boxes, like in the earlier games. This case later slightly repeats itself in Sonic Generations, where only Classic Sonic's acts feature them normally in Item Boxes. In Nintendo 3DS version of Sonic Generations, however, Modern Sonic can also use Invincibility, with both types of acts having monitors with Invincibility. Also, while Invisibility is available to the player in normal gameplay; in the Nintendo 3DS version of Sonic Lost World, players can share Invincibility power-ups by using the Miiverse in Wii U version. Invincibility makes appearance both as a regular and Equippable Item in Sonic Runners. When the player gets it from the Item Box, it creates aura of small stars around the playable character.
- Several games in the series are known to have own related themes, which are not renditions of the game's main themes. A notable example is in the US version of Sonic the Hedgehog CD. There's one recurring theme from Sonic Adventure (titled "Invincible ...No Fear!" in soundtrack), that is later repeated and having more fast tempo in Sonic Adventure 2 (titled "Still Invincible... No Fear!" in soundtrack). Sonic Advance 2 and Sonic Advance 3 are known to have own independent theme and Sonic Rush games have fast paced mix playing as BGM.
- The Invincibility theme from the original Sonic the Hedgehog has been the most reused one through the Sonic the Hedgehog series, as it can be heard with a more fast tempo in Sonic the Hedgehog 2, Sonic Advance and two different variations for Classic and Modern Sonic are featured in Sonic Generations.
- Invincibility theme in Nintendo 3DS version of Sonic Lost World is instrumental mix of Sonic Heroes song from the same titled game, making it one of rare times in the series using main theme from different game.
- Super transformations of playable characters are usually granted invincibility during normal in-gameplay, though it only lasts for as long as the transformation can be maintained, which is tied to the Ring count that decreases one per second while in a Super State. Usually the player can be stunned by some of bosses attacks, but in several games, more powerful attacks are able to damage the playable character on his super-form and even lose some Rings.
- In Sonic Heroes, when the player gets the invincibility and tries to run into enemies, it does not affect the enemy until the player attacks it. In Sonic the Hedgehog (2006), the player is unable to defeat enemies by walking forward towards them while having Invincibility; instead, the player walks through the enemies without doing any damage.
- In Sonic & Knuckles, due to Sonic and Knuckles sharing different color palettes, the stars have red coloration instead of blue, when the playable character is Knuckles. The Water Shield and S monitor both share this trait.