The Day of the Doctor

When The Day of the Doctor comes into play,
remove all your creatures. Then put that many
4/4 The Doctor creature tokens with flying on
the battlefield.
When The Day of the Doctor leaves the battlefield, sacrifice all The Doctor tokens.
Then return the removed cards into play.
Our future depends on one single moment of one impossible day. The day I've been running from all
my life. The day of the Doctor.