I have a great strategy for all metal energy users.
First you will need four metal energies, two steelixs,
two any kind onix (except brocks),2-4 pokemon marches
and four darkness energies. You get you onix out put a
metal energy on him dont attack it will hurt you 10.
Then attach a darkness, steelix, or metal energy
again. Buid your onix/steelix until it gets 2-4 metal
energies, and 2-4 darkness energies. If you do this
then use tail crush it does 30 on tails (normally) and
50 heads (normally) so with the 2-4 metal and darkness
energies it will do this 40,50,60,70 on tails with the
darkness and metal energies. 60,70,80,90 on heads with
the great combo.

To get this I've used pokemon marches, computer
searches, and the odds. Metal reduces damage by 10
darkness applies 10 damage to the defending pokemon.
So darkness does 10 to any pokemon without dark but
the metal erases that damage making do all damage to
the opponent and not you.

--Billy Gibson