Okay, there's been a lot of controversy over just how useful the Darkness cards are.  Let's review.
I use PKMN for Pokemon, dmg for damage, and AP for Attack Power (How much dmg an attack does). (My
comments are in parentheses):

Murkrow

D Mean Look - Opponent can't retreat as long as Murkrow is active. (Too bad this isn't powered by C.
It's a waste of D energy, and Switch can beat it.)

DC Feint Attack - Choose an opposing PKMN and do 20 dmg.  Not affected by W, R, Powers, or effects
on the defending PKMN.  (Now, at first, I thought this negated the +10 AP facet of Darkness Energy.
But it doesn't.  The card specifically says that Feint's AP is not affected by effects ON THE
DEFENDING PKMN.  The AP boost of Darkness E is an effect on Murkrow, not the defender, so you would
do 30 dmg [if you're using real Dark E]. Sweet!)

Sneasel

C Fury Swipes - 3 coins, 10x heads dmg. (Perfectly ordinary, max 30 dmg for 1, not bad.  But if you
use D to power it, you can do max 40 dmg, and do 20 if you get at least one heads.  That could ruin
a day right there.

DD Beat up - coins x # PKMN in play = 20x heads dmg. (Whoo! It's Dark Wiggly!  Let's assume a full
bench of 12 PKMN. No heads = 0, but if you're using pure Dark, than 1 heads (1! out of at least 2!)
= 40 dmg (20 + 10 Dark + 10 Dark) 5 heads with this attack will kill ANYTHING! (5x20=100 + 20 Dark =
120) Oh yeah, Sneasel's a bad dude.)

Using Rainbow Energy as Dark (or Steel/Metal)

Rainbow energy can become any color.  Dark and Metal are consider base energy types, but not base
energy cards, like Grass or Fire.  That means that if you use Rainbow Energy to power an attack that
require D, then you will just do the base damage, not adding D dmg credit, since it does not have
the property of Dark Energy that adds dmg. It's an imitation.  Of course, it also does not do dmg to
a non-Dark (well, 10, but no Dark Poison).  This also applies to Steel Energy.  You'll get the
Energy Cost paid, but not the -10 dmg benefit, or the -10 AP drawback for non-Steel.

Ditto's special circumstances.

Ditto's transform power essentially make all energy attached to it Rainbow, without the damage.
That means it can turn any energy into D or M energy to pay costs.  If the energy is not REAL D or M
energy, however, none of the added effects that would normally apply will apply.

Example, Ditto vs Sneasel

If Ditto has 2 energies of any type attached, then it can use Beat Up, as if it had DD.  It's dmg,
however, will max out at 240 (assuming full benches and all heads), instead of Sneasel's 260.  So
Ditto must flip 6 heads to do max dmg. (Trust me, it's not a sure thing.  I narrowly escaped a Big
Eggsplosion where the Exeggutor had 10 energy on it)  Of course, it would only take 3 heads to beat
a Sneasel's 60 HP. But, if Ditto has real D on him, he gets the same benefits as Sneasel would.
However, Ditto should handle real Darkness Energy as if it was radioactive, since, if the defending
Dark is KOed, or Ditto is Benched, he will become Colorless and be Dark Poisoned. Yikes!  Ditto
could, of course, use a DCE and still do Beat Up.  Ditto has an easier life than real Darks and
Steels.

TO REVIEW:

Murkrow's Feint Attack is boosted by Dark Energy.
Murkrow can attack the Bench (With Feint)
Sneasel's dmg with Beat Up can beat anything with 6 heads (using RaRa), 5 (using DRa), or 4 (using
DD).
Dark Energy boosts AP, Rainbow Energy masquerading as Dark does not.
Rainbow energy can become Dark or Steel Energy, for the purpose of paying energy costs.
Ditto can do Dark attacks with any Energy.
Ditto can be seriously harmed by real Darkness Energy, by the same methods that hurt him otherwise
(benching, defender switch).

The lessons from here can also be applied to the Metal types.  Try it out.

A question : Could Ditto protect itself from the drawbacks of Dark or Steel energy by turning it
into soething else (say Fire or Grass)?  Only Wizards knows for sure.  If yes, then it could not
turn it Dark for the attack (getting the boost in AP), then turn it basic afterwards, avoiding the
damage, since Ditto would be stopped immediately following the attack and the energy would be
"locked" into Dark until Ditto's next turn.

Scott Parker
sparker@triad.rr.com