I've liked Rapidash since it was first printed. It has good art and its attack name is Ring of Fire, other than that I thought it was trash. While at Nationals, I was beaten out of Top Cut by someone playing MegaPlume, who was using Roserade UL and ever since, I have been wanting to find a good partner for Roserade.
The Basics.
Rapidash: Ok, so this is your mane attacker. Ring of Fire is a pretty bad attack, the 50 damage is nice, but the important thing is that it is a tribute to Johnny Cash. Oh and the fact that the defending Pokemon can't retreat is the only reason this deck works, so I guess I should mention that too. The burn is a cool little addition, and the fact that it can't be Confused is great against fellow Roserade players. Roserade: So this is the card that makes that atrocious excuse for a card Rapidash work. Obviously, you are going to need Rainbow Energy, making the opponent Confused and Poisoned at the same time is key. Both of those conditions are pretty nifty, and with Rapidash using Ring of Fire after Energy Signal, your opponent's active will be Confused, Poisoned, Burned, and they can't retreat out of it. That is pretty cool, because they will take 50 damage, plus Poison, plus Burn, that is 80 damage (60 with the wrong answer on a coin flip), and they only have a 50% chance of hitting your frail little Rapidash, which makes up for its low low HP.
Magnezone Prime: This thing is a little draw monster to make up for how slow this deck could be. It is pretty important to get it out by turn 2, which shouldn't really be that hard. Magnezone lets you draw for the rest of the game (kinda), and makes a great back up attacker with lost burn, since you are already playing Rainbow Energy.
Now that the main attackers/important things are covered, I think I can discuss some various techs that you can add to personalize your own list.
Options.
Weavile: This tech is alright. It is ok to disrupt your opponent early game, and is a good way to get rid of Switch.
Shaymin: I'm kinda surprised that I didn't put this in the Basics of the deck category. Roserade is a decent attacker in a desperate situation, but you really don't want your Rainbow Energy stuck on it. This allows you to move the Rainbows you attach to your Roserade to Rapidash, so you can get the lock down T2. It is allow great to move energies to Magnezone. I'll just cut this down to saying it is good.
Vileplume: Vileplume is cool because it makes it so they can't switch out of a lock, making it unbreakable. It helps against the Yanmega match up. I personally like Vileplume, but if you are playing it, Magnezone is much less useful, which can hurt you, because you need Rainbow Energy in your hand ASAP.
Various Babies: Tyrogue and Cleffa, cliche stuff. I guess they are good for stalling, if the defending Pokemon is still Poisoned and Burned, Cleffa is a good starter, if you don't have the resources in hand to get out a Magnezone.
Non-Obvious Trainers that I should probably mention.
Seeker: Pick up Rainbow Energies so you can continue to Energy Signal.
Defender: Rapidash is really really frail.
Victory Medal: Wanna here something weird? This card is actually not that bad. Plus you get to be playing Victory Medal, that's always fun.
Here some lists that I have tested, they are decent to work from, but I noticed they could use some work, and sorta die out late game. Just drop the things that are bad, and think of them as skeletons.
4-4 Rapidash
3-3 Roserade
2 Cleffa
1 Tyrogue
2 Shaymin
Pokemon: 19
4 Pokemon Collector
4 Professor Oak's New Theory
4 Pokemon Communication
4 Junk Arm
4 Pokeball
2 Research Records
2 Professor Juniper
4 Pokemon Reversal
2 Seeker
1 Switch
T/S/S: 31
4 DCE
4 Rainbow Energy
2 Fire Energy
Energy: 10
3-3 Roserade
2 Cleffa
1 Tyrogue
2 Shaymin
Pokemon: 19
4 Pokemon Collector
4 Professor Oak's New Theory
4 Pokemon Communication
4 Junk Arm
4 Pokeball
2 Research Records
2 Professor Juniper
4 Pokemon Reversal
2 Seeker
1 Switch
T/S/S: 31
4 DCE
4 Rainbow Energy
2 Fire Energy
Energy: 10
4-4 Rapidash
3-3 Roserade
3-1-2 Magnezone
2-1-2 Vileplume
1 Tyrogue
Pokemon: 26
4 Pokemon Collector
4 Professor Oak's New Theory
4 Pokemon Communication
4 Rare Candy
2 Professor Juniper
1 Copycat
2 Seeker
1 Switch
T/S/S: 24
4 Rainbow Energy
4 DCE
2 Fire Energy
Energy: 10
3-3 Roserade
3-1-2 Magnezone
2-1-2 Vileplume
1 Tyrogue
Pokemon: 26
4 Pokemon Collector
4 Professor Oak's New Theory
4 Pokemon Communication
4 Rare Candy
2 Professor Juniper
1 Copycat
2 Seeker
1 Switch
T/S/S: 24
4 Rainbow Energy
4 DCE
2 Fire Energy
Energy: 10
I'm going to answer some questions I'm sure I'm going to hear.
Is this deck actually fast? It sounds inconsistent.: This deck has such hardcore lightning fast reflexes, it could pick up your opponents fully reverse Kingdra Yanmega, and unsleeve it before they even notice what is happening. Nah, but seriously focus on setting up Magnezone first. Once that is out you can get everything else out in a turn, maybe 2 if you are unlucky.
How does this deck deal with _______ ? It has poor late game, and isn't all and all that good, don't except it to perform well at any tournament bigger than States.
Hey Vulpix, why do I hate you and your writing style of writing so much?: ... Whatever.
Are you just playing this deck because you can call it Rainbow Dash?: No. Ok maybe a little.
Edits: Houndoom Prime is an interesting option over Rapidash, you would have to reformat the list a little, but it may be worth it for the extra 20 damage. Burn is flipsy though.
Anyways I hope you enjoyed the first "article" I've ever written, it may not be too competitive of a deck, but it is a very fun play, and I would encourage testing it.
~ Vulpix Yolk