Rubee Savings and Loan
From the Super Mario Wiki
The Rubee Savings and Loan is a small company in Merlee's Mansion which is actually a bank that Mimi owns. Mimi employs Ackpows to supervise the slaves that Mimi captures. They must collect Rubees to pay off their time there. Mario must find Slim in the mansion and he can get one million Rubees to pay off his debt to Mimi, Mario being the only person to do so over the course of the game. Once this is done, Mimi is shocked to see that one person has paid the loan fully and apparently explodes. The Star Block can now be hit (using Slim to get between the bars of the cage it is in), and Mario, goes on to the next chapter.