Day of Darkness

Cast Day of Darkness only if you control a card
named Yami or Yamata No Orochi.
This spell can't be countered.
Demons get +5/+5 and have haste.
Non-Demon creatures get -5/-5 and have
last strike. (Those creatures deal combat damage
after creatures without last strike.)
At the beginning of your end step, exile Day of
Darkness.