Lives, also known as 1-Ups, are present in most Sonic games. They represent the amount of chances the player has to complete a game. When a life is lost, the player restarts at the previous checkpoint.
A power-up which grants an extra life to the player. Also, as a general rule in all the canonical games, collecting 100 rings also grants an extra life. Many mini games include getting an extra life as a prize, such as the gumball machine in Sonic the Hedgehog 3.
If a player gets hit and has one or more rings in their possession, they will lose all of their rings or some of them (in some games), but will not die. If the player is hit when they have no rings, they will lose a life and return to the last checkpoint or the beginning of the act. There are other ways to lose lives, such as drowning, falling into a bottomless pit, or being crushed, and in these cases, the player will lose a life regardless of how many rings they have.
As an Item box, the image on the monitor usually appears as the head of the character who is being controlled. This means that, depending on who is played as during the level, the appearance of the item box containing a life may change to the head of the playing character. The variety of images on an extra life monitor depends on the number of playable characters available. In later games, mug-shots on the item boxes were simply replaced with a "1UP" picture, disregarding who the playing character is.
In more recent Sonic games (Unleashed, Colors and Generations), which exclusively star Sonic as the player character, lives are not contained within item boxes and are simply a picture of Sonic's head.
Appears in basically all 2D and 3D games with the exception of non-canon games (Racing, Super Smash Bros. Brawl, etc.).
Classic 2D GamesEdit
Appears in capsule form and must be smashed or in Sonic the Hedgehog 4 by the homing attack.
GBA and NDS 2D GamesEdit
Appears as a capsule that only needs to be touched to obtain.
An item that must be hit to achieve.
Appears as a power up that must be smashed in order to be obtained.
Appears in a capsule that must be touched to obtain an extra life.
Appears as a 3D square, collected by simply touching it.
Appears in the temple puzzles and grants a permanent extra life to your count.