What accessory linked two Game Boys for multiplayer in 1989's Tetris?

The Game Link Cable linked two Game Boys for multiplayer in the 1989 version of Tetris. Each player used a separate Game Boy and Tetris Game Pak, with the two handhelds connected by the cable.

Nintendo’s Game Boy Tetris was notable not only because it made the puzzle game portable, but also because it was the first Game Boy title compatible with the Game Link Cable. In its two-player mode, players competed to stay alive longer than their opponent.

Clearing a Double, Triple, or Tetris could add incomplete rows to the other player’s stack. That competitive feature helped demonstrate why the cable mattered: it turned two normally solitary handhelds into a linked multiplayer system.

The other options belong to different Nintendo hardware contexts. The Super Game Boy played Game Boy cartridges through a Super NES, the Game Boy Printer produced physical printouts, and the Transfer Pak connected Game Boy software with Nintendo 64 games.