Here's a neat hidden feature for Magical Tetris Challenge's Endless Tetris Mode. Start a game in endless mode and tap A and B at the same time during gameplay. This will switch on a graphical display on the 2P screen that shows how many lines you have cleared (divided into singles, doubles, triples, and so on). Have fun.

To short the magical gauge, you must clear all the blocks. If you got it right, a ALL CLEAR! Sign will appear in your playfield.