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 and Peach must find Slim in the mansion and they can get one million Rubees to pay off their debt to Mimi, Mario and Peach being the only ones to do so over the course of the game. Once this is done, Mimi is shocked to see that two people have 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 and Peach go on to the next chapter.