Here's how it works: Little cartoon viruses are floating inside a playfield of 8x16 squares. Two-sided vitamin capsules fall slowly from the top of the bottle. Use the joystick to move and rotate the capsules so that four items (viruses or capsule halves) of the same color are contiguous in a row or column. With skillful play, you can set it up so that capsule halves created after a combination create new four-in-a-row combinations. There's also an addictive deathmatch mode, where you can use such chain reactions to attack your opponent.
U.S. Patent 5,265,888 covers Dr. Mario, but as of 2002, Nintendo has not enforced it against amateur software developers.
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