Background

Countries began passing laws regulating simulated gambling in video games by the end of the 2000s, and Pokémon's Game Corner and its slot machines were not exempt. The Korean release of Diamond and Pearl removed the slot machine minigames from the Game Corner and replaced them with a simple script that gave the player coins upon interacting with the machines. This change was also implemented in the European release of Platinum to comply with PEGI guidelines. (Towell 2009)

When Gold and Silver were remade, Voltorb Flip was created to replace Goldenrod City's and Celadon City's slot machines for all localizations outside of Japan. Since it isn't based on a real casino game and it doesn't cost in-game currency to play, it doesn't constitute simulated gambling. (ESRB)

Voltorb Flip is a much better game than the slot machines it replaces. The sole downside for HeartGold and SoulSilver is that you can no longer buy in-game coins since you can only gain and never lose them playing Voltorb Flip. It's often described as a combination of Picross and Minesweeper, but to be honest I don't see the Minesweeper resemblance beyond the lose condition.

Gameplay

The game board is a 5 × 5 grid. The right and bottom edges of the game board display information about the corresponding row to the left or column above, respectively. The top number in each box equals the sum of all tiles in the respective row or column, while the bottom number represents the number of Voltorbs. A game is won by revealing all 2 and 3 tiles; it is not necessary to reveal all 1 tiles. The score is calculated by multiplying all revealed tiles; Voltorbs correspond to zero and revealing one loses the game. Upon losing, the game level decreases to the level equal to the number of tiles revealed before revealing the Voltorb. The game's level is not decreased if at least as many tiles were revealed as the current level.

Tiles can be marked with possible values by right-clicking or activating marker mode. Marker mode is activated by clicking the bottom button in the column to the right of the game board and is intended for playing on a touchscreen. The buttons above toggle which values are marked. Note that tiles cannot be clicked if they are marked with only Voltorb and must be unmarked first or additionally marked with a number.

The row of buttons below the game board toggles several assist options:

1. Reduces the row sums and column sums every time a tile is flipped to show the sum of the unflipped tiles only
2. Automatically flags tiles that are definitely Voltorbs in certain circumstances; not all definite Voltorbs will be flagged
3. Automatically flags "dead rows" that contain only Voltorbs or 1s
4. Ensures that losing decreases the game's level by no more than 1
5. Guarantees the generation of at least one safe row or column featuring no Voltorbs

An excellent strategy guide is available on The Cave of Dragonflies. (The Cave of Dragonflies)

Hotkeys

• Toggle Voltorb marker: V or Numpad 0
• Toggle 1 marker: 1 or Numpad 1
• Toggle 2 marker: 2 or Numpad 2
• Toggle 3 marker: 3 or Numpad 3
• Toggle marker mode: Left-Shift or Numpad 5

^{(Fun fact, I had no idea that the HTML canvas feature existed when I programmed this game! Please don't look at the source code.)}

Footnotes