Unknown Item

Three Unknown Items are found in Metroid: Zero Mission. Initially, they are unusable by Samus as upgrades. Instead, they allow certain blocks bearing images of the associated Unknown Item to be destroyed. Until the player defeats the Chozo Hieroglyphic, the Unknown Items appear as question marks on the inventory screen. After defeating it, the Unknown Items' true identities are revealed to be the Gravity Suit, Plasma Beam, and Space Jump.

The Unknown Items were based on the Sacred Treasures from Kid Icarus, which used the Metroid engine. They were the Mirror Shield (Gravity Suit), Light Arrows (Plasma Beam), and Wings of Pegasus (Space Jump). All three were required to go to the last level of the game, and were not usable before that level.