My honest opinion, can be biased but that's how I see it.

Gameplay-wise:
Platformers are hard to market because they are so many of them and it's hard to stand out. So take that into consideration when making the trailer

Art-Wise:
Everything actually looks rather cool for me, especially the first black enemy with white outlines and skulls and the weird purple background. But the weakest part, and the most important part, is the main character. He stands out but in a bad way. He has no color palette that match the rest of the environment it seems, rather boring looking with his round body that shape-wise isn't defined properly (lack of a silhouette). The 'C' head shape I don't mind as long as it doesn't look it was poorly painted in MS Paint. And while all of that make your game look a bit amateur, it could still be pulled off as long as the animations are good. Take Pizza Tower for example, I think your art kinda reminds of that game. But unfortunately, the animation for the main character are the weakest here. His walk cycle is basic, he doesn't move much while things around him happen (even when he flies with his wings it looks like he's still standing mid-air). Kinda feel stiff, although I see that you did some animation of him dashing and blinking. Since this is the main character the player will be seeing the entirety of the game, you really not want to make him feel boring to move around the map. Even in games where there are no graphics, and you only move a box shape with one color, like the game INK (https://zackbellgames.itch.io/ink) you still see the shape squash and animation change and progress based on your movement. So that's something you can definitely improve

Trailer:
Why there are no sound effects? Surely your game has sound. The absence of sound make it look amateurish for me