Hi, Pojo! Matthew here...
I was just wondering what would happen if somebody had a Clefable as their
active Pokemon and their opponent had Exeggutor. If the person with
Clefable used Metronome, could they keep flipping coins, or would they have
to have a certain amount of energy?

The Clefable player would have to count the amount of energy on the Clefable and flip that many coins.  It would not even look at the energy on Exeggutor.

Scott