Panharmonicon

If an artifact or creature entering the battlefield
causes a triggered ability of a permanent you
control to trigger, that ability triggers an
additional time.
Once I said to a scarecrow, "You must be tired of
standing in this lonely field." And he said, "The joy
of scaring is a deep and lasting one, and I never
tire of it." Said I, after a minute of thought, "It is
true; for I too have known that joy." Said he,
"Only those who are stuffed with straw can know it."