Hitting the 'ILLUSION' bonus will score you ‘1500000’ points.
Basically if you're ultra skilful and with a bit of luck this is possible to do. First you have to get 3 blinking tiles on the screen; next you must connect all three in a row, horizontal or vertical. After it's been connected, the screen will flash with a spark bursting out and the word 'ILLUSION - 1500000' in the centre of the screen.
Note: This Bonus is also in GameBoy Advance Zooo.