Activate Clock of Omens by tapping itself and King Macar, untapping King Macar.
King Macar triggers, exiling any creature an opponent controls and creating a Gold token.
Activate Clock of Omens by tapping the Gold token and King Macar, targeting King Macar.
Holding priority, activate the Gold token by sacrificing it, adding ({1} magic symbol) .
Activate Karn by paying ({1} magic symbol) , causing target noncreature permanent an opponent controls to become an artifact creature until end of turn.
Resolve the Clock of Omens ability, untapping King Macar.
Repeat from step 2.
Results
Exile all nonland permanents your opponents control.