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 of their choice.
When there are no lands on the battlefield, sacrifice Mana Vortex.
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.