Starting with the set that should do well against Heracross. Will edit other cards into post in an hour or two.
Natu Lv. 12 -50HP- [P]
Basic Pokémon
Picture: Natu is perched on the branch of a Cheri Berry tree. It has a Cheri Berry held in its beak. Leaves and berries make up the background and surround the Natu in the foreground.
[.] Link Minds
Move up to two [P] Energy cards between your Pokémon in any way you like.
[P][P] Telekinesis
Choose 1 of your opponent's Pokémon. This attack does 20 damage to that Pokémon. This attack's damage isn't affected by Weakness or Resistance.
Flavor Text: Natu found in the wild often organize the Pokémon around them into social groupings. Oddly, the Natu are rarely the leaders of these groupings.
W- [L]+10
R- [F]-20
RC-[C]
Xatu Lv. 28 -80HP- [P]
Stage 1 Pokémon: Evolves from Natu
Picture: The camera is viewing Xatu from above as it flies over a forest. Far below Xatu (but still above the forest) is a flock of Swablu.
Poké-Power: Shake Off
At the beginning of your turn, if Xatu is affected by any Special Conditions, flip a coin for each. If heads, remove that Special Condition.
[P] Hunt and Peck 10+
Search your discard pile for a Pokémon Tool or Technical Machine and attach it to Xatu. (This does not permit you to have more than one Pokémon Tool attached to Xatu.) If you do, this attack does 10 damage plus 30 more damage.
[P][C][C] Temporal Blast 60
Discard a card from your hand. Then, draw a card from the top and bottom of your deck. (If you can't discard a card from your hand, this attack does nothing.)
Flavor Text: Wild Xatu are often stand-offish. Many researchers suggest this is due to their haunting visions of the future.
W- [L]+20
R- [F]-20
RC- [C]
Xatu Lv. X -100HP- [P]
Level-Up [Put onto Xatu]
Picture: Xatu's eye glitters with a red-violet aura; its outstretched wingtips extend beyond the frams on both the left and right towards the upper edges. The background glitters in a dark-violet to black haze.
Poke-Body: Foreknowledge
Prevent all effects of your opponents Poke-Powers, including damage, done to Xatu.
[P][P] Energy Rainbow 20+
Does 20 damage plus 20 more damage for each type of Basic Energy card in play.
[Put this card onto your Active Xatu. Xatu Lv. X can use any attack, Poké-Power, or Poké-Body from its previous Level.]
W- [L]x2
R- [F]-20
RC- [C]
Explanation: Xatu is a Pokémon of many effects and little damage. Xatu is great for helping your deck run more efficiently. Its Hunt and Peck attack is very useful for pulling TMs like Devoluter onto Xatu from the discard pile as disruption or Evoluter to help speed your deck. Also, Tools like Leftovers (to help bolster Xatu's low HP,) Bubble Coat (for against Lightning Pokémon,) or Energy Link (to help quick-charge Xatu) can be grabbed. All while doing quick damage for low cost. Temporal Blast allows you to get card advantage while getting rid of un-needed cards in hand, all while doing fair amounts of damage. And the Level X's Energy Rainbow has the potential to do fairly significant damage, particularly against decks that try abusing multiple types of energy (like Skittles or Galactic Toolbox.) Energy Rainbow would be expected to do 40 damage minimum, and 60-80 damage on average. Crobat G+Energy Link would also make it possible to abuse cards like Flint's Willpower to charge Xatu more easily.
Against Heracross (and its Level X,) Xatu's best combos include Volkner's Philosophy and Felicity's Drawing to discard Energy Link or Leftovers. Hunt and Peck would then do 60 damage to Heracross (80 to the Lv X,) preventing the use of Deft Disarming without Heracross KOing itself. Also, Temporal Blast is a guaranteed OHKO and Energy Rainbow is likely to get a OHKO as well (since the Lvl X requires 2 types of Energy that are not [P].) Xatu's low retreat cost and Stage 1 speed make Judo Throw less harmful, and Xatu's Shake Off makes Precision Strike less effective (assuming the Heracross can find time to charge it against Xatu.) Lastly, Xatu's ability to easily recover lost TMs and Tools (as well as Energy Link making it easier to keep Energy on Xatu) make Heracross Lv X's Massive Throw much less useful. However, because Heracross is generally speedy, can abuse Regirock+Stark's Mountain, and generally hits for high damage+at least the chance of Paralyzing Xatu or switching it, Heracross can potentially play around Xatu.
Back to back posts merged. The following information has been added:
(Ack, that took longer to type than expected!) Ok, and the card for Heracross to beat is...
Magnemite Lv. 11 -50HP- [L]
Basic Pokémon
Picture: Magnemite hovers along a rocky path. Pebbles are floating after the Magnemite, carried by its magnetic field.
[Poké-Power] Irresistable Magnetism
Once during your turn, when you put Magnemite from your hand onto your Bench, you may search your deck for a Special Energy card and attach it to your Active Pokémon. If you do, your opponent may search his or her deck for a Special Energy card and attach it to his or her Active Pokémon. Shuffle both decks afterward.
[L] Zap
Choose 1 of your opponent's Pokémon. This attack deals 10 damage to that Pokémon. (Apply Weakness and Resistance normally for Benched Pokémon.)
Flavor Text: Wild Magnemite often attract more trouble than they can handle. As a result, many seek out Trainers for protection.
W- [F]+10
R- [P]-20
RC- [C]
Magneton Lv. 26 -80HP- [M]
Stage 1 Pokémon: Evolves from Magnemite
Picture: Magneton is floating in a gym with its eyes squinted and static flaring in several directions. Dumbells and barbells are floating at odd angles around it.
[Poké-Body] Electro-Magnetism
Any [M] Energy attached to Magneton also produce [L], but only 1 Energy at a time.
[L][M] Magnetic Charge 20
During your opponent's next turn, neither the Defending Pokémon nor Magneton can be switched to the Bench by the effect of a Trainer card.
Flavor Text: Trainers often teach Magneton moves that use its hard, metallic body and magnetic powers to defend itself.
W- [F]+20
R- [P]-20
RC- [C]
Magnezone Lv. 48 -120HP- [M]
Stage 2 Pokémon: Evolves from Magneton
Picture: Magnezone hovers in a battle arena that is surrounded by stands full of cheering Pokémon fans. A researcher stands at the visible end of the arena, apparently giving a command to Magnezone. Magnezone is being struck by lightning and channeling it into a ball of lightning in front of it.
[Poké-Body] Metal Memory
Magnezone can use any attack, Poké-Power, or Poké-Body from its Basic Pokémon card or its Stage 1 Evolution card. (You still have to pay for the attack's Energy cost.)
[L][M] Magna-Ram 20x
Does 20 damage times the number of Special Energy cards attached to Magnezone.
[L][L][L] Ball Lightning 60
Flip 2 coins. If both are heads, this attack does 60 damage plus 20 more damage and the Defending Pokémon is now Paralyzed. If both are tails, discard all Energy cards from Magnezone.
Flavor Text: Trainers that are patient enough to train Magnezone find that it is a powerful, loyal companion.
W- [F]+30
R- [P]-20
RC- [C][C]
Magnezone Lv. X -140HP- [M]
Level-Up [Put onto Magnezone]
Picture: Magnezone is charging its electricity for an attack. Small sparks are radiating from Magnezone out of the frame. Magnezone's metallic body is polished to a mirror-like shine.
[Poké-Power] Wild Lightning
Once during your turn (before you attack), you may use this power. Magnezone's type is [L] until the end of your turn.
[L][L][L][L] Lightning Rush 80
Discard an Energy from Magnezone. If you discarded a [L] Energy, this attack does 80 damage plus 20 more damage. If you discarded a [M] Energy, reduce damage from attacks done to Magnezone by 20 until the end of your opponent's next turn.
[Put this card onto your Active Magnezone. Magnezone Lv. X can use any attack, Poké-Power, or Poké-Body from its previous Level.]
W- [F]x2
R- [P]-20
RC- [C][C][C]
Explanation: Most of the Magnezone line is fairly self-explanatory. It is a Stage 2 that you want to play the full line through (rather than Rare Candy-ing past the Stage 1) because of Magnezone's (and Magneton's) Poké-Body. This is especially true as Lightning Rush is even more brutal when discarding a Metal Energy that is also a Lightning Energy. Generally, though, the point is to use/abuse Special Metal Energy as much as possible. Also, I know that it is standard for Metal Magnezone to have a R weakness, while Electric Magnezone has the F weakness, but part of my set's premise involves the mixing up of multi-type Pokémon. For Magnezone, I wanted it to have a strong affinity to its Electric side, while still being Metal. Other combos include: Magnemite (SF) to reduce retreat cost, Multi Energy and Rainbow Energy to enhance Lightning Rush and Magna-Ram, Conductive Quarry to retrieve lost Special Metal Energy, etc.
As for the Heracross match-up, Heracross would make Magnemite's downside even more drastic, considering Heracross's Deft Disarming would allow you to remove the opponent's Special Energy while keeping your own. Strategic usage of Deft Disarming should, in fact, reduce the effectiveness of Special Metal Energy to nil. Also, because Magnezone really wants to level up normally rather than skipping the Stage 1, Heracross is able to deal enough damage to KO Magnemite/Magneton before it has the beefy 120-140HP. In addition, the chance that Ball Lightning could discard all of Magnezone's Energy means that a powerful 120 damage Massive Throw from Heracross Level X is a real possibility.