The Great Cataclysm

Put a time counter on Cataclysm. On your next
upkeep remove a time counter. Once the last
counter has been removed, each player destroys
all permanents except for 1 creature and 1 land.
"The Cataclysm was not one event, it was many.
Lands rose and fell. The sky rained fire, ash, and
worse things. The seas rose and then retreated. It is a miracle that any of us are still here." —Apollyon