Mana Burn

Implement rule 300.3 of the 2009 MTG Comprehensive Rules: "When a phase ends (but not a step), any unused mana left in a player's mana pool is lost. That player loses 1 life for each one mana lost this way. This is called mana burn."
{5}: Each player taps all untapped lands.
"I will make you take Mana Burn! I swear to God!"