This was a super chill last game to play for today before bed. I love just wandering around as this little dude exploring the mountainside. Your thumbnail is absolutely gorgeous, I think it's the best one I've seen in the jam so far.
As some of the other comments pointing out, the main thing affecting your game is that the pixels crucially need to all be the same size for the aesthetic to gel, I made the same mistake in my first pixel art game. What I do now is decide early what the game's "working" resolution will be, then I choose a canvas size for my main character accordingly, you can easily look this info up for other games to get an idea.
Let's say you go with a 16 x 16 character. Besides the landscape, that 16 x 16 is now your reference for everything else in the game (a good choice since the main character is always on screen). An elephant twice as big as the player? Okay, let's use a 32 x 32 canvas this time and fill it up. A little rock? Maybe I'd even keep it 16 x 16 for convienence, but just remember to take up less space in the canvas, then drop them both into a test scene to check the size works, or even keep your player on a different layer to compare while drawing. No scaling allowed! I hope that clears it up, it took me a minute to understand at first, but now I can't unsee it.