When you cast this spell, counter it unless you sacrifice a land.
At the beginning of each player's upkeep, that player sacrifices a land.
When there are no lands on the battlefield, sacrifice Mana Vortex.
10/1/2009 When you cast Mana Vortex, its first ability triggers and goes on the stack on top of the Mana Vortex spell. The triggered ability resolves first. When it resolves, you either sacrifice a land or you counter Mana Vortex.
10/1/2009 Mana Vortex’s third ability is a “state trigger.” Once a state trigger triggers, it won’t trigger again as long as the ability is on the stack. If the ability is countered and the trigger condition is still true, it will immediately trigger again.