Perhaps you are thinking of the "Lottery Corner" found in Jubilife City. This is a minigame where you can purchase lottery tickets and win prizes.
Here's how it works:
1. Purchase tickets: You can buy lottery tickets for 100 Pokédollars each from the vendor in Lottery Corner.
2. Pick your numbers: You choose three numbers between 1 and 10 for your ticket.
3. Draw the winning numbers: Each day, a set of three winning numbers is drawn.
4. Check your numbers: You can check your tickets against the winning numbers at the vendor.
5. Prizes: The number of matching numbers determines the prize you win.
Prizes:
* No Matches: No prize
* 1 Match: 500 Pokédollars
* 2 Matches: 10,000 Pokédollars
* 3 Matches: 100,000 Pokédollars
Tips:
* Increase your odds: You can buy multiple tickets to increase your chances of winning.
* Check the winning numbers daily: The winning numbers are drawn daily, so be sure to check them each day.
Let me know if you have any other questions about Pokemon Diamond!