Cradily - Grass - HP120
Stage 1 - Evolves from Lileep
[G] Life Explosion: For each Energy attached to this Pokemon, search your deck for a Stage 2 Pokemon and put it onto your Bench. Shuffle your deck afterwards.
[G][C] Spiral Drain: 60 damage. Heal 20 damage from this Pokemon.
Weakness: Fire (x2)
Resistance: Water (-20)
Retreat: 2
And I should also mention Lileep.
Lileep - Grass - HP80
Restored - Put this card onto your Bench only with the effect of Root Fossil
Ability: Call of the Ancient
Once during your turn (before your attack), if this card is in your discard pile, you may place it on the bottom of your deck.
[G][C] Spiral Drain: 20 damage. Heal 10 damage from this Pokemon.
Weakness: Fire (x2)
Resistance: Water (-20)
Retreat: 2
Obviously, Cradily card has some huge hurdles to overcome, but you can't deny that life explosion has some serious potential (even if it's not a top tier deck). You can put any combo of stage 2s in your deck, but don't need the lines. Best of all, you control what you start with. You can make it so you're sure to start with a big EX or some kind of defensive pokemon (Sigilyph) while still playing those stage 2s.
The biggest problem I see is the attack cost of life explosion. You need at least one grass energy to work with it. Blend only works with a few other types and prism only works on basics. I thought of a few solutions.
The first is Mew EX. Mew not only gets around the prism energy problem, but it also saves you the hassle of retreating in and out of Cradily. And of course, copying the attacks is
The second solution is to use stage 2s with colorless attack costs. Off the top of my head, I can think item lock Dragonite (PF), supporter lock Stoutland (BC), Seismatoad (PF) Exploud (PS) and any other Round attacker (who knows, maybe round decks will have a chance?), and I'm sure there are more I forgot about.
Lastly, you don't have to attack with your pokemon, you can just use them for their abilities. I don't think I need to explain all the useful abilities.
As for all out grass pokemon, the one I think should work the best is Royal Heal Serperior (BW). You can easily get 3 or 4 of these out and make your main attackers (mainly Genesect EX) near impossible to KO . Not only that, but the attack is very useful. Say you have a powered up Mew EX that's going to get knocked out next turn. You can copy leaf tornado, do some damage, and move the energy off of Mew to conserve it.
For backup attackers, there's PF Beedrill, who benefits greatly from constant healing (60 for :grass: plus two stasis conditions). There's also PS Torterra, while mediocre on it's own, can become a tank that will need a lot to OHKO it with both damage reduction and healing from serperior.
Those are just a few ideas. Don't know how good they'd be, but I would be surprised if someone doesn't break this card.