Russian Roulette

Protection from everything
({p/r} Equals mana on all battlefields, tap all)
When Russian Roulette enters the battlefield
put a 6 counter on it
-1 counter at end of controllers turn
{p/r}: add +1 to counter
(this action can be done by any player on their turn)
When counter reaches 0 all players lose half
their life rounded down, counter starts again at 6