This is Sonic Sudoku, a ROM hack by RetroKoH and CCB357.

This hack is exactly what the name suggests! It's Sonic, but you're playing Sudoku... while you're playing Sonic!

If you aren't familiar with Sudoku, here is a quick rundown of how the game works. You're presented with a 9x9 grid that you must fill with numbers from 1 to 9. To complete the puzzle, you must fill in the grid so that each number appears exactly ONCE in every row, ONCE in every column, and ONCE in every 3x3 sub-grid. In Sonic Sudoku, you fill in the grid by collecting numbered flags in each stage. Which numbers will fill in which spaces? I'm glad you asked!

The HUB room's Sudoku Grid is divided into nine (9) smaller 3x3 sub-grids. Each of these blocks is colored to suit the Zone that it corresponds to. You can use transporters to enter a Zone's Warp Room. From there, you'll find rings for each Zone's Acts! Each of the sub-grid's rows corresponds to an Act in that Zone. This means that the top row belongs to Act 1, the middle row belongs to Act 2, and the bottom row belongs to Act 3. If you collect numbered flags in that Act, their numbers will be entered into their respective places in that Act's row, provided they belong in that row to begin with. You'll see this happen in real-time in the RESULTS screen. Once you complete a zone's sub-grid, you have the option of entering a Giant Red Ring leading to a FOURTH ACT, fighting that zone's boss, and earning a Bonus Coin. These coins don't serve a purpose, however (At least, not yet...).

You may also buy numbers using the HUB's Ring Exchange. The first number costs 100 Rings, with each subsequent number costing 50 Rings more than the last. Your Ring count will be retained between stages, so feel free to replay and rack up Rings as you wish. If you get hurt, you'll only lose up to 50 rings, but if you die, you'll lose all of your rings. Shields found along the way will help you, and they are also retained between stages. Collect a Blue Shield to unlock Elemental Shields!

Sonic's abilities include:

• Spin Dash (Hold down without charging to cancel freely).
• CD Peelout (It works exactly as it does in Sonic CD).
• Air Roll (Press Jump mid-air while not in a ball to roll up. You can even use this to curtail your vertical momentum if needed).
• Drop Dash (Default double-jump technique... and YES, you CAN transition from Air Roll to Drop Dash).
• Elemental Shield Double Jump abilities (No Insta-Shield though).

This ROM hack is built off of S1Fixed, a modded version of Sonic 1 with a wide variety of bugfixes and modifications. The biggest changes to this hack are the HUB, the Sudoku Table system, the Results screen, and various gameplay elements such as the removal of lives, and the expanded HUB elements. Level layouts are nearly identical to the original Sonic 1 (with the exception of Scrap Brain Zone), though some adjustments have been made in various areas.

Finally, if you somehow get stuck in a level, pause the game and press A to return to the HUB.