There are three levels to the mini-game: Beginner, Intermediate, and Expert. The level of difficulty influences the cost, the size, and the amount of traps within the game.
The Beginner difficulty costs 30 Rupees to play, and consists of twenty spaces in a 5x4 grid. Of these spots, four are bombs. The grid is guaranteed to hold a number of both Green and Blue Rupees, with a small chance of a Red Rupee.
The Intermediate difficulty costs 50 Rupees to play, and consists of thirty spots in a 6x5 grid. Of these spots, four are Rupoors and four are bombs. The grid contains mostly Blue and Red Rupees, while Green and Silver Rupees are fairly rare.
The Expert difficulty costs 70 Rupees to play, and consists of forty spots in an 8x5 grid. Of these spots, eight are Rupoors and eight are bombs. Most spots contain Red Rupees, and occasional sightings of Blue, Silver, and Gold Rupees have been observed.
Once all Rupees are discovered or Link digs up a bomb, the game ends. Any Rupees Link digs up are added to his wallet; and should Link manage to dig up all the Rupees, he obtains a Rare Treasure as an additional reward.
Should Link run low on health, a seat is provided nearby where he may regenerate hearts lost to bombs and talk to Mr. Tubert.
The layout of the area is fixed as soon as Link enters the mini-game, so it's possible to dig up a bomb straight off.
The type of Rupee in a dig spot identifies how many Bombs and Rupoors are in the eight spots around it, as follows:
Green Rupee: 0 spots
Blue Rupee: 1-2 spots
Red Rupee: 3-4 spots
Silver Rupee: 5-6 spots
Gold Rupee: 7-8 spots
This makes it quite hard to determine exactly how many spots are covered. Link can uncover all spots around Green Rupees without harm, while it's probably a very good idea to avoid all spots around a Gold Rupee.
Rupoors identify as a bomb for the purposes of which type of Rupees surround it, and will subtract 10 Rupees from Link's current total, but do not end the game. Therefore, it's possible to use Rupoor spots as a means of finding bombs or other Rupoors nearby more accurately.