Unlike Tetris, TetriNET can only be played in multiplayer mode, with two to six players. The twist in this Tetris variant is that powerful special blocks can be collected from the playing field and used to either boost your own position or hurt an opponent's. These special blocks change the focus of the game from merely amassing Tetrises to a strategic mixture of clearing lines and hunting down powerful blocks.
Players cannot arrange the order of special blocks in their inventories - they must use the blocks they collect first. The inventory has a maximum size of 18. If the inventory is full, and new special blocks are collected, they are discarded. The developers claim that allowing players to immediately access their most powerful blocks would remove strategy from the game.
- Add Line (a) - adds a line to the bottom of target player's field
- Clear Special Blocks (b) - turns all special blocks in a player's field into normal blocks
- Clear Line (c) - clears a line from target player's field
- Block Gravity (g) - pulls down all blocks vertically, filling any gaps in the playing field. Lines created in this manner aren't added to opponents.
- Nuke Field (n) - clears the entire playing field of a player
- Block Bomb (o) - if target player has an (o) in their field, "blows up" the eight surrounding blocks and places them in random locations on the field
- Blockquake (q) - shifts all lines in a player's field either left or right one block
- Clear Random Blocks (r) - randomly removes up to 10 blocks from a player's field
- Switch Fields (s) - swaps the entire playing field with a player
- While the (c) block is normally used defensively on a player's own field, it can be useful in the early game to prevent an opponent from picking up a special block or racking up a Tetris at the bottom of their field.
- The (b) block should be saved until an opponent has a (g), (n), or (s) in their field.
- The (q) block is devastating to anyone aiming for a Tetris.
- The (o) block, while tricky to use, can ruin another player's early game. It loses its effectiveness in the late game.
- The (g) block is by far the most powerful in the game. It can be used defensively, to save a field that is otherwise lost. More important, it can be used offensively. A player holding a (g) block can shoot for Tetrises without fear of being hit by a (q) or (r), as the (g) allows them to quickly recover once a straight four-piece begins to fall. In the hands of an expert, one or two (g) blocks can sometimes be enough win a game.