The tiles with the hidden properties.
In Mari0 and Mari0: SE, the Default Tilesets contain tiles with hidden tile properties. They are "hidden" in that, normally, tile properties are plainly visible as part of the tileset itself, while these properties only exist because the code references a specific Tile ID.
The hidden properties are too specific in function to be of much use in regular custom tiles anyway, but they are a consideration when replacing the default tilesets using Custom Graphics; since the hidden properties cannot be disabled, the tiles at those IDs must be taken in the context of their hidden properties.
Blank[]
The only tile with this property is Tile #1, which serves as a blank tile. Despite having a purple checkerboard appearance while selecting it, it shows nothing when placed. The only purpose of reskinning it would be for the amusement of the user.
Bridge[]
- Main article: Tilesets#Bridge
In 1.6 and below, the bridge under Bowser and the chain holding it had a hidden tile property. Due to the lack of Custom Graphics in these versions, applying it to other tiles wasn't possible. It was changed into a regular tile property in Mari0: SE
Used Block[]
An example of modifying a Used Block.
A Used Block appears when Mario empties a breakable block or a Coin Block of its contents. There are quite a few Used Blocks, as seen in the SMB tileset. The Used Block shown varies based on both the level's spriteset and the item that was in the block. Using Custom Graphics, one can modify the Used Block to produce various effects. Of note is setting its property to Breakable or Coinblock, allowing the player to hit the block indefinitely for as many items as they want.
2×2 Block[]
The only used 2×2 block in the game is Tile #136, which is the giant portal tile's top right piece by default. It is a shortcut for placing the entire 2×2 block. Using it places Tile #137 to the right of Tile #136, Tile #138 directly under Tile #136, and Tile #139 to the left of Tile #138.