These are alright, but need some work.
Fireball- Pretty good, actually, but the shading should be less linear, and more like that of Darkfire's shading.
Inferorb- Ultimately needs a lot of work. Like Fireball, the shading is too linear. The eyes and mouth is adequate, but I would advise giving it more shape.
Fireskull- Like Inferorb, this one needs lots of work. The "mouth" is in a position that doesn't look right. I would advise putting more effort into the top of the fire, you just copied and pasted, which shows a lack of effort. The position of the eyes are all wrong, and should be more parallel to the mouth. The name is also very unoriginal.
Crushfish- Honestly, I can't say that effort was put into this. I would advise putting some time into the body shape, rather than putting 6 seconds into it by using the circle tool. The eyes, which I believe are from an existing Pokemon sprite anyways, are not in the right position. I would move the left eye much more to the left, to make it more realistic. The mouth is just stolen from a Gyarados sprite, and is in the wrong position. This is why you should create your own mouth (unless you're making a splice). Like most of the others, the name is unoriginal
Devitomb- This, however, is a turn from your usual sprite. The form, color, shading, everything, is perfect. This one actually looks professional. The name is also fitting and original.
Fireray- I'm disappointed, actually. You went back to just using the circle tool, and adding a random part. I have a feeling that the bottom "foot" is from another Pokemon, I feel like I've seen it before. However, the shading is top-notch and accurate, which shows a huge sign of improvement from Inferorb/Fireskull.
Darkfly- This is basically the same as Fireray, accept you just changed the face and added wings. However, the shading is pretty good, and you seem to have gotten the hang of that. Also has an unoriginal name.
Dragondark- This one is pretty good, but the dark hole for a mouth should have some shading or a separate outline. Once again, the name is really unoriginal. I'm also pretty sure that the wings are from Skarmory.
Leafsnake- The top is great, I must compliment that (but I do feel as if I've seen it before). However, the bottom is just a collection of copied circles, showing a lack of effort.
Spiritiny- You must like Spiritomb quite a bit. Like Devitomb, this one is perfect with form, shading, concept, name, everything. Great job!
Darkfire- This one has great shading and the arms are great too, but I would change the mouth, or at least remove the lit area near it. I would also make two new legs, rather than copy-pasting Fireray's "leg." This brings up another problem, as the left leg should be less wide and/or have a different pose to show the angle. However, it has the same circle and name problem.
Your recent sprites show great improvement, but I would advise to keep working and use more custom shapes rather than just using the circle tool over and over again. Keep it up!
~Prof. W.