Gym Heroes has two cards called Brock's Onix.

I want to look at the common version (card 69)

First the stats (with thanks to Bret Larwick for the spoiler)

100 HP, Grass Weakness, No Resistance, Retreate Cost 3

Bellow [1]  Flip a coin.  If heads, the Defending Pokemon is now Paralyzed.
Rock Throw [1FF]  30 Damage

First the good news: A common card with 100hp, and a decent attack.

With 100hp this guy can take a hit from a fully powered Wigglytuff,
Blastoise or Chansey and still be there next turn. It takes three shots from
most haymakers to knock this Onix out. This is a seriously tough pokemon.

Now the bad news. It takes three turns to get enough energy on Onix to do
any damage. Unfortunately this means that Onix gets knocked out one turn
after you've got him powered up.

Actually, no it doesn't.  Use one Brock's Onix to stall and you have three
turns to power up an Onix on your bench, and to find a switch to rescue your
stalling Onix. You don't even need rare trainer's; plenty of Bills and
Professor Oaks in your hand will speed you to the necessary cards. Add in a
couple of Pewter City Gym stadium trainer cards to bypass fighting
resistance and you have a seriously powerful combo.

The high retreat cost, and high energy cost to deal damage, stop this
Brock's Onix from being one of the great pokemon. This is still the best
value for money card since Jungle Jigglypuff and I will be putting 3 in my
anti-hay deck.

Thanks for listening

Words of Wisdom to highclere@excite.co.uk