Koskun Falls | Magic: The Gathering
Formats Koskun Falls is Legal in
Official Oracle Text for Koskun Falls
Creatures can't attack you unless their controller pays for each creature he or she controls that's attacking you.
Official Rulings for Koskun Falls
10/1/2008 : This has the supertype world. When a world permanent enters the battlefield, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter the battlefield at the same time, they're both put into their owners' graveyards.
2/1/2014 : Unless some effect explicitly says otherwise, a creature that can't attack you can still attack a planeswalker you control.