Drakuni, Lord of Broken Time

Unpredictable (When this creature enters the battlefield, roll a six-sided die.)
Whenever you roll a 1 on a six-sided die, return Drakuni, Lord of Broken Time to the bottom of your library.
Whenever you roll a 6 on a six-sided die, roll the die an additional time. If you roll a 5 or 6, take another turn after this one.