I've been reading a few of the top 10 lists and top 10 Challenge cards, and
Sabrina's Golduck is either 2nd or 1st.
Here are some comments about this card:

"HOLY COW! This pokemon combos wonderfully with Alakazam, giving Swap decks
the power two heal, and to attack. Also gets around Mime's power, since it
isn't damaging Mime. It's placing damage counters on it."
-The Mind of Sabrina - Paco 10/3

"First, get out Sabrina's Golduck. It's first attack, no coin flip required,
allows you to remove one damage counter(only ONE)from each of your bench to
the defending pokemon. "But what if only one of your bench has damage?" you
say. For all you pessimists, use Alakazam to move one to your whole bench
and Active. That's 60 damage a turn. But how do you get damage quickly?
Minefield gym gets you 20 damage if you flip tails when putting a basic on
your bench.(Wizards didn't write it correctly, but I know the
translation)See? Instant Wiggly damage for less than your paying now!"
-Gym Challenge Strategy - Q 10/11

"1. Sabrina's Golduck
   Coooool! As always, Psychic gets a splashable Water monster out of  
Golduck. With Challenge!, you can load up the bench, then your       Active
can use a bench- damaging attack, like Dugtrio's Earthquake.    Retreat that
Active in favor of Golduck. Damage Shift not only heals your bench,
it does 60 to the Defending Pokemon! All of that for an attack cost of
PP!"
-Gym Challenge Overview - The Rocket 10/11
1. He needs a full bench for a good effect.
2. All of the basics are Gust Of Wind bait.
3. He needs a source for damage. I know you can use self damaging attacks,
but look at all that
complicated retreating. I also happen to know that you can trick the
opponent in to mindless attacks,
and then out of nowhere comes Sabrina's Golduck returning the damage. Lets
see what that takes to
work. You have to bench the Sabrina's Psyduck, and attach PP to it, taking
two turns. The opponent
has two turns to notice it and either gust it out, or destroy anyone with
damage. Its not that hard.
And if the Sabrina's Golduck happens to successfully come out, all you need
to do is to stop the attacking,
and prepare for a one hit KO on the bench.

Thanks for reading. SIglesias
Feel free to reply to me at SIgelsias@earthlink.net