Invincible

Invincibility (無敵), also called as Invincible and Invincible Barrier, is a general power-up present in Sonic the Hedgehog series, that can be found in Item boxes with either showing four-pointed stars or colorful sparkling shield on the marking. When the player obtains this power-up, the playable become immune to most 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. Invincibility has been staying as mostly untouched, like Super Rings, Power Sneakers and other Item Box power-ups, but in several games, it has have other different features. While Invincibility has not been featured as generally as before, it is seen to be used in the latest games as well.

Overview
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 length of Invincibility can usually run about 15-20 seconds before it fades out, where the length of the Invincibility differs with 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 Muteki Boxes (無敵BOX). Once picked up, the player can activate it whenever he/she wants, which makes the player invulnerable to obstacles, while 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), 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.

Trivia

 * Several games in the series are known to have own related themes, which aren't renditions of the game's main themes. Notable ones are such as US version of Sonic 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 original Sonic the Hedgehog has been the most highly reused through the series, as it can be heard with more fast tempo in Sonic the Hedgehog 2, Sonic Advance and two different variations for classic and modern Sonic can be heard in Sonic Generations.
 * Super transformations of playable characters can also have invincibility during the normal in-game, which is also only temporary, as the ring count decreases one per second all the time. 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 doesn't affect the enemy until the player does attacks on him. In Sonic the Hedgehog (2006), the player is unable to defeat enemies by walking forward towards them while having Invincibility; as a result, the player only walks through the enemies without doing any damage.