Great Blue is on a standard 5x3 reel grid. The background is a deep blue ocean with bubbles floating up to the surface. The reel itself has a different shade of blue from the water in the background, with numbers from 1 to 20 appearing on both the left and right hand sides. Of course, it depends on how many lines you play. You can choose to play on one, or use the full 20.
Oyster shells are game dispersions that can easily appear anywhere on the shaft. If you happen to encounter three or more, you will activate the Great Blue bonus game. You will automatically start 8 free spins, using a 2x multiplier, so you need to choose two of the five oyster shells to win more free spins and/or multipliers. At best, you can win 33 free spins and/or a multiplier of up to x15.