Perfect Diamond

Perfect Diamond is a fast-paced puzzle game created for the original NES from the 1980s. Slide puzzle blocks into the grid to fill lines. Play any of the 3 single-player game modes, or battle a friend or CPU in local multiplayer.
ROM file included for those who want to play on emulator or on a real NES via flash cart. (Right-click the game in your Steam library, click Properties/Installed Files/Browse)
Mechanics:
Pieces slide forward on their own. You can move them right or left, and spin them in either direction.

When a piece reaches a position where it fits, it drops into the grid.

If a piece passes the grid without dropping into it, it is discarded and comes back 2 pieces later. If the same piece passes the grid a second time, it's game over.

When a line in either diagonal is filled, it is cleared and points are awarded.

Additional points are awarded for clearing multiple lines simultaneously, clearing lines in both diagonals simultaneously, and fitting a piece snugly into a hole.

Single Player Game Modes:
Survival: Try to score as many points as you can while the speed increases ever 11 lines.

Prudence: Take it slow and get as many points as you can with 250 pieces.

Velocity: Disregard score, clear 50 lines as fast as possible!

Multiplayer Game Modes:
Blocks: Score points to send blocks to mess up your opponent's grid.

Speed: Clear 11 lines to increase your opponent's speed.

Both: Enable Blocks and Speed together.