Thank you i haven't had anyone tell me that before!It gave me my greatest boost of confidence ever:)
I don't think you suck at all! And your more recent submission is an improvement over these, so you're getting even better.
You haven't posted very much work yet, and in what you have posted, I see no really big flaws (aside from all the empty space in this piece xP). You're struggling with AA, but AA is an advanced technique! As I mentioned in my previous post, try to aim for colours that are halfway in value between the two you're trying to blend. it's fine to be a little off, but if it's too close to one or the other in value, it won't help the piece look smoother. In your more recent Isaac head, for example, the dark red you're using to AA between the blood and the outline is too similar to the blood, so it doesn't really help. A darker colour would be more appropriate.
A possibly related issue - when adding new colours, make sure they pull their weight at 1x zoom! If they're indistinguishable from another colour at 1x, merge them, or make your new colour more distinct. For example, I like the detail of the outlines on your Isaac heads being lighter at the top, but that's only visible if I zoom in to 7x or so! Against the white background, both colours just look black, the purple is just too similar to the black. You'd need a much darker background or a lighter purple for the effect to be noticeable without zooming in so much.
Thanks! I really need to keep practicing since im still beginner :\.Btw what thing do i have to practice more?I know i suck but what's the worst?
You don't need all that empty space around them. It just makes it harder to zoom in, since it pushes the heads off-screen.
The bottom one looks blurry, you added a bit too much AA on it. Some of the others also have AA where it's not needed. 45-degree lines and vertical/horizontal lines do not need AA, as they already read as "smooth". Adding AA there just makes the piece blurry.
In the top five faces, your AA colour is too light to really make a difference. You even went as far as adding a whole new colour for the AA, when what you really needed was your skin shadow colour. I think the only ones of these requiring distinct AA colours are the 2nd and 3rd from the bottom, where your external AA is too dark. As a general rule, the value (brightness/darkness) of your AA colour should be about halfway between the values of the two colours you're smoothing between. The hue doesn't matter much.
Here are edits of the top and bottom heads that reduce the blur where you overdid the AA, add some smoothness where you under-did it, and eliminate some of your barely-discernible colours. I hope these will help you!
You might notice I removed some of the interior details in the top head's eyes and the bottom head's mouth. These details looked nice zoomed in, but weren't visible at all otherwise. I'm of the opinion that such details aren't really useful.
I would reccomend to do a more personal approach to these sprites, as they are almost identical to the ones shown in-game. Also as Eishiya said you should get rid of all that white space, in fact you can do it without needing to delete the piece.
I feel like these are the main issues that keep it from being uploaded to the main gallery.