Unlock the custom game mode

Set the

• size and maximum size of the square
  
• count of different colors

Further you can set the

• timer before a new line spawns
  
• incremental decrease of consecutive timers
  
• and where these lines will be added
  
• count of locked blocks
  
• a rotationspeed of the square
  
• minimum number of blocks that are required for a complete line

and then play this setup for as long as you like

Chose your prefered level. From pretty simple like 5x5 with 3 colors or slightly more challanging 8x8 with 8 colors.
Find your sweetspot and stay there as long as it's fun.