Assist Block

Assist Blocks are golden blocks that appear in Super Mario 3D Land, New Super Mario Bros. 2, and Super Mario 3D World. There are two types of Assist Blocks: one that contains an Invincibility Leaf, and one that contains a P-Wing; these items help the player reach the end of the level, and they appear near the beginning (or midway) of the stage after losing a certain number of lives in that stage.

Super Mario 3D Land
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. However, Luigi cannot obtain one unless Mario skips a normal world level (for example, by Warp Zone), as these blocks don't appear in the Special Worlds, and don't return if the level in question is beaten.

Exclusive to Super Mario 3D Land, the P-Wing Assist Block appears after Mario loses ten lives in a stage. Using the P-Wing takes Mario all the way to the end of the stage, in front of the Flagpole.

If an Assist Block appears in a stage, any stars on the current save file will not sparkle (similar to the effect of the Super Guide Block from New Super Mario Bros. Wii).

New Super Mario Bros. 2
In New Super Mario Bros. 2, only the Invincibility Leaf Assist Block returns. However, unlike in Super Mario 3D Land, it turns the player into the White Raccoon form (rather than the White Tanooki form), it will always appear if five lives are lost in a level (regardless of whether or not the stage in question has been beaten), and it will disappear if any stage with one is cleared without using it (restoring the sparkles on the current save file's stars as well).

Super Mario 3D World
The Invincibility Leaf Assist Block appears once more in Super Mario 3D World, working as it did in Super Mario 3D Land. However, the number of lost lives needed to make it appear is based on the number of players: five for one player, 12 for two, 18 for three, and 24 for four.