Finally got around to playing this! I was considering making a video, but still have a cold and not sure if I have the right set up. ANYWAYS, good demo. I'll try to say things that haven't been said here already or are worth reiterating.
Visuals and everything are nice, great job. Obviously is an early setup so not all sfx and such will be in (Like wish the cards would make some noise when collected). Lighting is pretty good too. Only issue art wise is perhaps making things more apparent, especially in terms of depth. The clouds at the end could be hard to make out when trying to jump over them.
Menu is aesthetically pleasing but needs work in terms of representation and order. I could see myself and others confused by where certain things were, such as the clothes. Maybe also making it more obvious what section of the menu you're in. So if you're equipping weapons, highlight that area of that menu. Just better indications to really make it crystal clear what's being done.
Controls well, but one thing I noticed was a lack of Jump Buffering. Well, that might be the wrong term, since that's usually for press jump a few frames before you land so a new jump registers. What I ACTUALLY mean, is jumping off ledges. I think having a few frames after the player is "off ground" to press jump so they can make precise jumps would be REALLY helpful. Especially for players who aren't that great at platforming. This demo featured far more platforming intense obstacles than Paper Mario normally did.
I'm not a fan of the text scroll. I've yet to deal with programming text boxes, but I do have some rules for what to do/don't. And since this is an RPG, having good text boxes is crucial. But I'm 100% sure ya know that, cause this is Paper Mario! Where they use wacky text effects like wavy animated text and such. Just make sure it scrolls left, and that the words generated at the end of a line START on the next line; that stuff BUGS me when devs don't do that. Adventures of Pip doesn't do it. You'll see a word spelled out at the end of a text line but then it gets too long for the text box so it suddenly jumps to the next line all weird and stuff and eeeeewww...
Btw I played this demo without cutting any flowers so I could see if the RatBee thing would change dialogue. They didn't... 0/10
Kidding, but speaking of cutting things down, hmm. I didn't do it much cause I had seen my friends the Console Warriors play the demo so I didn't bother, but they used the Sword to cut down the grass. A lot. Now cutting it down with the sword is fine, good way of finding secrets. But there's a LOT of grass, and you're a 2D character slicing the sword in a 3D space. So it feels sort of awkward to slice all this grass for secrets. It's not like Zelda where you can quickly get around and slice multiple blades of grass. I think something you could do is add something to the sword later on to perhaps "spin attack" and slice multiple grass. That would be very convenient. Or combine it with the Spin Ability.
Speaking of which I have mixed feelings with this Spin. It's sort of like Paper Marios, but it's also not. It definitely has more platforming use, but feels far less controllable. In PM I'd use it all the time, jump to cancel out of the end lag, land and repeat using it. So I tried to see if I could find a similar technique. And I did! But even so, I think this ability needs better control, or perhaps something to outright stop you from falling off so easily. But my earlier point about the jumps might help there.
Anyways the technique I found was to spin, then immediately jump. When I landed, I could spin again just about instantly AND it cancels out the daze part if I jump/land before it happens. Perhaps if you could teach this to players or make its use more apparent and easy to control, then it would be even better for getting around. But at the same time, I'm mixed because this ability in PM wasn't something you equipped (well, there was one that made it longer). It was natural, so it makes me question if this should be a slot in the first place and not a natural ability.
Anyways Hammer feels good. Paper Airplane is good enough, but wish it crafted you at the top of the character rather than the bottom. I'm guessing you had it this way to not have to mess with changing hitboxes on the ground. So I think the feel of you becoming an airplane needs work.
That's about all I got to say. Other than perhaps the sign/menu at the beginning likely wasn't loaded properly because the game pauses for 3 seconds to load it all, then it's all good from there. I think there are a lot of things that could be done to enhance performance, but I'm certain you can figure that out. Also respawns are... not the best. If you can, trying adding something in the character object that detects where it was last on solid land, then spawn back there like PM. Certain pits you fall in can even spawn you in NEW areas you hadn't reached yet which is weird.
Good Demo to test the waters! Definitely has potential!