I really dont know if this is the correct spot to post this but id figure it wouldnt hurt.
recently i did some tests on catching great marsh pokemon, as nobody has done this before (probably because its damn hard :P) and i figured it would help others if i would post my findings.
first of all, you will want to stand directly in front of the spot where the person asks you if you want to enter the great marsh, when you do one step it wont count as a step, then after talking and answering "yes" to enter the great marsh, then the game will do 5 steps for you and after that you are in the marsh. these steps dont count as real steps according to the step application so im reasonably sure that they wont mess with the frames.
then, when you enter you will notice 2 npc's and they move a lot :P this is the reason why great marsh pkm are so hard to abuse (i'd say its impossible to do on a regular cart because its so hard to hit your target frame)
anyway when you move in the swamp you will likely sink into it. at that point your X or Start will freeze which means you cant go to your bag or anything like that. you'll have to move left and right until you are on top of the swampy patch, at that point your X should work which means you are able to use sweet scent at that point.
the big problem however is that moving left and right will advance the frame too :P
so how can we catch great marsh pokemon then?
well its not THAT hard if you are using save states
first of all you need a spread with a high frame (+ 500 gives you enough time to stand in the grass and check your frame a few times)
this is mainly because the npc's advance the frame quickly, in my test I had hit frame 415 after 30 seconds without advancing the frame with journal flips.
the idea is to save state somewhere before your target frame ( you can use sweet scent to catch a pkm, then check its iv's to see which frame you landed on) then save state if you are before your target frame and then keep loading the save state until you encounter the pokemon you want.
hope this helps anyone, i highly doubt someone can do this without AR and save states, but it would be really cool if someone is able to do it without it.
if so let me know :D