Metal block

Metal Blocks are large, metalic blocks that are found in Paper Mario.

These blocks typically serve as barriers which block a path to either a new or hidden area. When Mario finds one of these blocks, he will be unable to break them using either a Hammer or a Super Hammer. Mario may come across some Metal Blocks prior to Chapter 5, but he will be unable to break them until finding the Ultra Hammer. Once Mario finds the Ultra Hammer during his expedition into Mt. Lavalava, he can then use it to break any Metal Blocks he may come across.

In Paper Mario: The Thousand-Year Door, a few Metal Blocks can be found in the Riddle Tower. Here, they cannot be destroyed, even with the Ultra Hammer; instead, Mario must solve a puzzle to eliminate them. Those ones looked more like they were brick.