Olkira, the Corrupter

When Olkira enters the battlefield, put a
Corruption counter on all creatures.
After two turns, gain control of all
creatures with corruption counters on them.
Then, sacrifice them two turns later.
At the beginning of your end step, if you control
no creatures, you lose 500 life and put all cards
in your hand, library, command zone, and
graveyard into exile.
"You call that a Cataclysm? Here, allow me."