The Tetris room is a room that is based in Tetris. The Kid travels here after defeating Snifit and falling in a hole. This room have falling Tetris blocks that The Kid must avoid. If you can't get up for too long, a giant pill from Dr. Mario falls and kills you.
To get to the passage that leads to Path to Kraidgief's Hideout, The Kid must jump on top of the blocks.