Decree of Immolation

As you cast Decree of Immolation, you may pay
an extra {2}. If you don't, sacrifice Decree of
Immolation at the beginning of your end step.
At the beginning of your end step, Decree of Immolation deals damage to each opponent equal
to the number of creatures that died this turn,
plus 1.
When Decree of Immolation is sent to the
graveyard from the battlefield, it deals 5 damage
to each opponent.
What is the oldest fire?