For those with Nintendo Switch online subscription, you have already been able to play Tetris 99 for free. However, you will now be able to extend the default content by adding in a paid DLC, and in this addition is the ability to play in an offline mode.
The Big Block DLC offers two different offline modes. One is a CPU battle which is very similar to the standard online game. In this mode, you are stacked up against 98 enemy bots. There is also a Marathon mode that allows the classic game of Tetris to be played in an attempt to beat a high score.
A third offline mode will also be up at some point later in the year.
The Big Block DLC is up for grabs right now and you can get it for $10.39.