Biorhythm essentially reads "Kill all players that have no creatures in play." The goal with the card, then, would be to remove all of your opponent's creatures but not your own, and then cast Biorhythm to end the game. But a
Wrath of God, a new creature, and Biorhythm all on the same turn will run you upwards of thirteen mana, which is a bit out of hand. And if you try casting them on different turns, your opponent may sneak some creatures out and ruin your plans.
The answer is a little-used instant from
Seventh Edition, Evacuation. For five mana, you can empty the board of creatures at the end of your opponent's turn, clearing the way for a fatal Biorhythm on yours. All you need to do is get one creature in play in the meantime, and
Squirrel Nest or a cheap
Llanowar Elves will take care of that requirement.
Anurid Brushhopper can also hide from the Evacuation, reappearing at just the right moment to win you the game.