Nothack's Otherplane

Nothack's Otherplane enters the battlefield tapped.
{t}: Add {c} to your mana pool.
{w}{b}, {t}, tap an untapped creature you control: Each player exiles two permanents he or she controls.
When each player owns sixteen or more cards in exile, each player sacrifices all permanents he or she controls, then returns all cards they own in exile to the battlefield under their owner's control.