Ember, World On Fire

When Ember enters, put a burn counter on each other creature and each player.

At the beginning of each end step, deal damage to each creature and player with a burn counter on them equal to the number of burn counters on them, then double the burn counters on each creature and player that took damage this way.

When Ember leaves the battlefield, remove all burn counters from each creature and player with a burn counter on them.