Played through it, its pretty good, although I would say the controls might need a bit of tweaking, or at least an explanation. I would assume that you tried replicating the old pizza tower beta move set, specifically with the weird high jump that you have to be still to use. Generally however the move set feels fine, the part I feel should use tweaking is how much you get stunned, if you hit a wall you get stunned, if you hit an enemy you get stunned, if you touch a pit you get stunned, if you roll into an enemy you get hit and stunned when normally you'd expect the enemy to die. Having some way to break out of the stun or at least having the stun scale with what your doing (so doing something like getting hit by an enemy would still give you full stun and lock your controls, but just bumping a wall only takes control away for a second or so). The biggest reason this is an issue is because of pits, I had so many attempts where I would be doing great but then accidentally bump into a pit when fighting an enemy or something and lose pretty much all my health cause I got stuck bouncing in a pit till I died.
I would also say that since the levels are missing any form of collectables that Wario land styled games usually do, such as WL4's gem pieces or keybird, that you don't really have the incentive to explore the level to actually progress, but I'm assuming that stuff like that is just absent as this is a 1 level demo and such collectables wouldn't make a difference, so I'm assuming you already plan to have items in the full game or whatever you plan to turn this into.
Overall pretty good demo, only things I could really think of just playing through it casually would be to reduce stunning, and also probably add more feedback to your gameplay (such as the combo bar making a noise when a combo breaks or an indicator for the level end thing starting the escape sequence.)
I would say this is probably a 7/10 or an 8/10 seeing as this is a demo.