Most of the LoZ graphics are very awesome. The style looks simple, but this don't mean that it's simple to make. They got all their bascs right and as I showed in the tutorial with the box, there is no difference between a simple style and a detailed style, if it comes to some of the very basics. Just to underline it: the
LoZ basics are done right (except stuff which looks better for their style, but that's about breaking and banding rules)
If you prefer SD3 or LoZ is also just personal taste, both games are done pretty professional.
I don't think it's very productive if you start working on enemies you will only see in one particular level in the game. It's more important to work on proportions and the general impression of size first. One of the most important things are proportions. Not only the proportions for one thing, but also the proportions from one thing to another (e.g. your molerat is kinda big compared to the chicken) and if you can name me something which is better fitting for the base scale as the main hero? The HUD and the main heros are the 2 most important things of every game - simple because they are displayed during the whole game. If the HUD or the char looks like crap, the game will look like crap. All the other stuff can be the most beautiful stuff ever, but it won't count.
Because of that I ask you once more. Why don't you want to start with the charakters? (Yeah of course drawing humans can be scary, but I think you can learn also a lot from it ... and RPG chars are really far away from humans and don't scary after all. You'll have to face this problem in some time).
I also won't concentrate on fancy stuff like "cleaning" lines first. It's just a huge waste of time as long as the basics arent right. If you ask me I won't be able to make out any difference between your fox 1 and 4 (1:1, just by glaring over it, I had to read and look at it longer).
Final details are just giving your art a polished look or a different style. You can Avoid banding, use AA and dither as well as every other pixel technique on a obvious wrong base, this won't improve the drawing.
Using these techniques on a base which is alright, let it look even better. (I don't say that it isn't possible to hide your poor drawing skills behind pixel work, because it is (!), but everybody who knows the basics or thinks 3 dimensional will see your mistakes within the first glare.
The good thing about 3/4 charakters is that they also don't need to be exactly in this perspective. This would also be a pretty bad idea, because it looks odd (ceased by the not very natural viewing angle) but it doesn't mean that you should avoid depth of space everywhere it's possible. Drawing is about form control, pixel-art is about pixel-control. This can get really challenging.
If you take a look of my edit, I removed all the stuff you don't need necessarily. I simple used 6 colors and the outline is black. I worked at the perspective and the forms and tried to add depth. BTW I really love the design of the creature. Now it would be time for AA and co.
If you look at both sprites you can see the differences at the first glare.
It also don't hurt to add eyes, or turning the whole sprite a bit. This just emphasizes the impression.
And keep in mind that enemies are animated, the movement is even more important than the quality of the sprite.
comparison:
sprite: