While the Gym Heroes set has provided some great cards for many types of
decks, the type it seems to help the most is the Status Effect decks.  Here
is, in my opinion, one of the best status effect Pokémon available.

Erika's Gloom
Stage 1 - Evolves from Erika's Oddish
Uncommon
Type - Grass
60 HP
Weakness - Fire
Resistance - None
Retreat - 1
Level - 24
(G) Healing Pollen
Flip a coin.  If heads, remove 4 damage counters from Erika's Gloom. If
Erika's Gloom has fewer damage counters than that, remove all of them.
(GGG) Magic Pollen
Flip a coin. If heads, the Defending Pokémon is now Asleep, Confused,
Paralyzed, or Poisoned (your choice).

60 HP is fairly low for a first stage, but Healing Pollen will help keep it
in the game for quite a while. The main reason this card is so good (in my
opinion), is the second attack, Magic Pollen.  The ability to choose which
status effect you want is great.  Is it a high-retreat Pokémon with no
energy?  Poison it and watch your opponent scramble for a Switch!  Do you
only need only one more turn's worth of damage for a KO?  Paralyze it so that
you aren't damaged, and to keep your opponent from retreating.  Does it have
a lot of HP?  While Poison can work, Confusion keeps them from attacking and
makes them hurt themselves instead of you!  Do you feel like taking a chance
that they won't attack for quite a while?  Put them to sleep and hope that
they flip tails to see if they wake up.

The Disadvantages:
Both attacks require coin flips.  The only way to truly succeed with this
Pokémon is to rig the coin, and I'm not recommending that!

What it Evolves From:
Many a Pokémon with potential was ignored because of a bad basic.  In my
opinion, Erika's Gloom doesn't have that problem, but to convince you, here
are the two Oddishes that Gloom can evolve from:

Erika's Oddish
Basic Pokémon
Uncommon
Grass
40 HP
Weakness - Fire
Resistance - None
Retreat - 1
Level - 12
Pokemon Power: Photosynthesis
All Energy cards attached to Erika's Oddish provide Grass Energy instead of
their usual type.  This Pokémon Power works even while Erika's Oddish is
Asleep, Confused, or Paralyzed.
(GG) Poisonpowder (20)
Flip a coin.  If heads, the Defending Pokémon is now Poisoned.

Photosynthesis is useless if you want to evolve into the level 24 Gloom,
because it requires all grass energy.  Poisonpowder is fairly good.  You can
Poison a Pokémon, then evolve and inflict one of the other status effects. 40
HP isn't at all good, and there are plenty of fire Pokémon waiting to tear
this guy apart.

Erika's Oddish
Basic Pokémon
Common
Grass
50 HP
Weakness - Fire
Resistance - None
Retreat - 1
Level - 15
(G) Blot (10)
If there are any damage counters on Erika's Oddish remove 1 of them.
(1G) Sporadic Sponging (20)
If Erika's Oddish has any damage counters on it, flip a coin.  If heads,
remove 1 of those damage counters.

This Oddish will certainly last longer.  Between the higher HP and the
healing attacks, you may not have to evolve it as soon as the level 12 one.

The choice between these two depends on what your deck and your personality
are like.  If you want to get in there and deal a lot of damage, never mind
if you get hurt, then the level 12 Oddish is for you.  But if you want a
Pokémon that can stay in the fight for a good, long time, then the level 15
Oddish is for you.  While everyone has a right to their own opinions, I
personally would chose the level 15 one. 

Just for fun, I decided to make up a deck using this line of Pokemon:

Miracle Powder

Pokemon x18
4x Erika's Oddish level 15 
3x Erika's Gloom level 24 - The backbone of the deck.
4x Venonat    
3x Venomoth - No matter how many sets are released, Venomoth will be used and
loved for its Poison and Confusion.
4x Rocket's Scyther - An improvement over the original.

Trainers x22
3x Oak
4x Bill
4x Computer Search
3x Blaine's Quiz #1 - It's really just three extra Bills.  I mean, who knows
Scyther's length?
4x Secret Mission - This thing is too good to pass up.
4x Gust of Wind - What deck shouldn't have this?

Energy x 20
20x Grass Energy

There you have it - A Gym Heroes Status Effect Deck.  Now go out there and
make it a feared Archetype!  (Okay, so it's not that good, but it's still
worth trying.)

~Kate

Questions?  Comments?  Improved versions of the deck I listed? Send it all to
smartypantskf@aol.com.
Hate mail also goes to that address. Just as you can't improve in Pokémon
without losing, you can't become a better writer without criticism.