1up!

1up! is a passive item.

Effects

 * Grants an extra life.
 * On resurrection, the mushroom that follows Isaac will disappear and Isaac will respawn in the previous room with all his previous Red Heart containers at full health.
 * If Isaac has no Red Heart containers, he'll respawn with 1/2 Soul Heart instead.
 * The 1up! mushroom begins following Isaac like a familiar upon pickup, but doesn't do anything.

Seeds
LDPB D0QG ( adjacent to spawn, first Secret Room to left from spawn, unless you have unlocked) CWSQ TNM8 (first Secret Room right from spawn)

Trivia

 * This is a reference to the Mario franchise, where collecting a green mushroom would give you an extra life.