From the Super Mario Wiki
Super Blocks are blocks that contain a spinning blue disk that appear in Paper Mario. Similar to Merlon's power in Paper Mario: The Thousand-Year Door, the Super Block upgrades Mario's partners. There are 16 blocks scattered all across the Mushroom Kingdom, with each of the 8 partners being able to upgrade twice. The fortune teller Merluvlee can tell where the Super Blocks are.
Each of Mario's partners can be upgraded twice: the first time to a Super Rank and the second time to an Ultra Rank after Mario receives the Ultra Stone from Raphael the Raven in Chapter 5. After Mario receives the Ultra Stone, he can choose to Ultra Rank a partner even if all partners aren't at Super Rank yet.