Don't pick this against DDD. The first transformation is very cramped and you'll be getting grabbed a lot and set up for quite a few edgeguards. The second transformation is completely flat on the bottom with walk of edges. Well, at least it's spacious.
The third transformation isn't that bad. The tilting is annoying but managable.
First transformation is all about maintaining control of the stage. As dark said, it's cramped. Keep your opponent out from being underneath the two platforms. Either keep them off the stage, or in the air with juggling. I don't like this part very much. I think trying to space yourself can become problematic here.
Transition stages you should continue as if you were on the center of final d. If they're high enough on damage though, dancing blade ending forward for a kill off the side.
Second part is my favorite out of all of them, but still a bit of a pain for being so large. Maintain control of the bottom and just generally stall below them until they come onto the bottom. Because it's so big the only way you can reliably get K.O.'s here is from the walk off, and even then I find it difficult since it's pretty obvious when you're trying to go for it and the stage allows for a good deal of running.
Third section is....Well nothing changes except for the tilting. It's nothing huge, but if you can stay on one side and let it tilt toward you. The lower Marth is the better since it means you can land faster from your aerials and enemy will likely have less attacks to hit you with since it's a weird angel. If you're on the uphill though, dtilt is pretty fun to use since it comes up a bit higher, but it doesn't shield poke now so meh.
I give this stage a 6/10. Marth does alright here, but not great.