RE: Poison Ivy
Good job with the Magius tech, it's often over looked for this deck.
Remove
Espeon Prime
3-1-2 Vileplume
2-2 Houndoom Prime
2 Rare Candy
3 Professor Elm
2 Professor Oak's New Theory
3 Twins
1 Copycat
1 Seeker
4 Grass Energy
1 Pokemon Collector
Remove : 28 Cards
Add
2-2 Roserade
1 Leafeon
1-1 Mismagius
3 Sage's Training
3 Professor Juniper
2 Plus Power
2 Pokemon Communications
3 Junk Arm
3 Pokemon Catcher
1 Unown [Return]
2 Psychic Energy
2 Rescue Energy
Add : 28 Cards
What was removed?
Pretty obvious stuff, Vileplume hinders you more than it saves you in this case. Espeon needs to have a Leafeon on bench for it to be any good and with Magius, Roserade, and other attackers, Espeon might not be the greatest of ideas to place onto your bench. My suggestion would be to simply accept the fact that dealing with Gothitelle is not going to be easy, with or without Espeon. Should you kill off another, it's easy to respond to your Espeon with a second Gothitelle. It's not even played that much so there isn't much of a need to tech against it.
Copycat, simply put, no.
Elm's are slow and outclassed in this case by communications.
Seeker is pretty good, I'd probably run one since all of your energies get dispersed by Magius, not to mention you also have Unown [Return] to grab any energies off of a Roserade. The reason why I suggest it is because it's a searchable energy return which can help you out a lot when you need the energies.
Twins, no point, this deck wasn't meant to fall behind.
Houndoom Prime, my problem with this card is similar to Espeon, what is there in the format that would get you really worried to the point you'd need to hit 150? With something like Houndoom that again sits on the bench and doesn't do much useful, that spot could be better taken by a back-up Leafeon or a saved spot for when you need to scoop energies from Roserade with Unown in a pinch. If you're really attached to it or think it will save you, I would keep it at 1-1 but I def. wouldn't rely on it.
The grass energies, they're nice to have but you can't move them around with Energy Trans from Magius, only reason I dropped the count it to put in more Psychic to increase the usefulness of that ability.
Why these cards to put in?
The point of most decks that can't hit super hard (Magnezone, Reshiram, Zekrom) is to take prizes off of things that they can kill a lot easier. There isn't much point in spending a bunch of resources to wound something badly, when they end up knocking out two of your pokemon to do so. A 2-1 prize trade leaves you behind and making the battle very uphill for you from then on. Rather than doing that, take advantage of the low energy cost of Leafeon and how quickly it sets up.
Catchers are there to grab set up pokemon and knock those out with Miasma Wind after placing Rainbow to Roserade. 100 damage + 10 from poison should KO a lot of those set up pokemon before they can get to their last form. Granted Rare Candy does speed thing up quite a bit, but being able to catcher pokemon they don't want to have in their active makes them waste resources to get it out of there, essentially buying you an extra turn of attacking.
Making use of the poison damage can go very well with Pluspowers as well since in the case of the dragons, you would hit for a total of 110 + 10 from poison damage. Upon the end of their turn (barring Eviolite'd basics) the poison damage racks up and knocks out their pokemon coming to your turn again. If you don't quite like Pluspowers, consider Rocky Helmet as it puts them in a similar situation and forces them to retreat to something else or attack with their active, giving you a prize as well.
Junk Arm - Staple in decks that run a lot of trainers, too good not to include.
Junipers, Sages - Since this deck is pretty speedy and there are a lot of cards that are trainers, you shouldn't have to worry to much about discarding them. It's actually better to have them in the discard so you can junk arm for them later rather than trying to have to dig through your deck to find it when you really need it. Having said that, these two cards will help you get through your deck a lot faster and will greatly increase the chances of grabbing that extra energy that you need or extra catcher/junk arm that you need to maintain the control of the board.
Rescue Energy for increased recovery since Miasma Wind takes one colourless energy to attack. If recovery is still an issue, consider Super Rod.
Extra Magius line for increased consistency.
Roserades because it's a part of the deck.
Finally, Unown [Return]. Great tech in this deck because like I mentioned above, he is a searchable energy return. You can collector for him when you really need to grab him out, or you can communications for him as well. Play this with Seeker should give you more than enough Rainbow energies that you can consistently Miasma Wind for at least 110 damage per turn.
That's what I would suggest and I probably wouldn't do much else for that deck. There isn't much point to teching in specific cards against other match ups, like Reshiram, or Zekrom for example. There isn't much that you could tech in at this point that would not only DRASTICALLY improve your match up against those decks, but also wouldn't drop consistency of your deck. It's better to run a deck without a lot of techs, playing it and tweaking it to be as consistant as possible. Hope that helps.
Also, I'm not sure if you were aware or not, but by placing Rainbow Energy onto Roserade, it counts as BOTH psychic and grass energy, thereby giving the effect from Roserade twice. Once for poison and once for confusion.