Haven't checked my post in awhile and just read through some of the comments. Thanks for the input!
I'm planning on dropping a Rescue Stretcher for Hoopa (Shining Legends). Not sure it'll be good enough as a staller though. Rescue Stretcher (and Plumeria) I'm usually not too excited to see, though Plumeria has occasionally saved me in a pinch.
What are people's thoughts on using Choice Band instead of FFB? On the one hand, CB lets you OHKO Lele (and other basic GX Pokemon) with a Berserk, on the other, FFB saves you from a banded Golisopod from OHKOing your Marshadow. I almost feel like I should drop both Plumeria and 1 FFB and add 2 CB and a third Guzma. Or possibly drop 1-2 Strong Energy. Not sure. I'm planning on taking this deck IRL to a tournament this weekend and want to tweak it to make it as good as possible. Don't want to change too much necessarily since I have a lot of experience with this current build.
I would go with the FFBs, I justify it by thinking that a FFB + Strong energy = a Choice band anyway but with the added benefit of +40HP. I would definitely recommend adding in a Magearna-EX and a Shining Mew, those 2 cards are indispensable in a variety of match-ups. Discard Shining mew as fast as possible to load any combination of special energy onto your Marshadow's, it has come in clutch in a few matches for me. Magearna-EX will protect your energy and prevent status effect/discard attacks as long as you have a rainbow energy. Just today I was able to protect myself from Trevenant Break's "Silent fear" attack with Magearna-EX. It also prevents Toxapex's "Super intense poison" attack for example and a variety of paralysis attacks. Magearna also doubles as a metal type attacker who can OHKO Gardevoir-GX, Sylveon-GX, and Ninetales-GX.
I definitely recommend adding a third Guzma and third Field blower as Garbotoxin is a deal breaker for this deck and you don't want to have to discard energy for retreating. I personally drop the Sycamore count in my deck in favour of Psychic's Third Eye. I also found Acerola to be very helpful at times to save a Marshadow and get the right energy off one and attach it to another.
I really want to add Zoroark-GX to my list, it has so much potential in this deck as both support and an attacker. But the cards online and offline are just too pricey at the moment. I'm gonna wait until the full art box is for sale.