The Assist Block are golden blocks that appear in Super Mario 3D Land. Two types of the Assist Block can be found: one will contain an Invincibility Leaf, while the other contains the P-Wing. These blocks are meant to help the player reach the end of the level, and will appear near the start of the level after the player has lost a certain amount of lives on that level.
The Invincibility Leaf Assist Block only appears after Mario loses five lives in a single stage. Once Mario collects the Invincibility Leaf, he transforms into White Tanooki Mario and becomes invincible for the entire stage. When he has lost ten lives on a level, the P-Wing Assist Block will appear and take Mario to the end of the level.
When Mario and Luigi get to the Special Worlds, the Assist Blocks won't appear in them.
Assist Blocks would return in New Super Mario Bros. 2. When a player has lost five lives in one level, the Assist Block will appear at the start of the level or at the Checkpoint Flag. When hit, the Invincibility Leaf will come out.