I don't know how to do the dropdown yellow bar thingies...but I do know about art, so here goes.
This first critique applies to nearly everyone that has art on here, including the three current examples. I've noticed that in the realm of fanart, very few artists even consider the ground area in their compositions. I usually see figures/creatures/items just floating in a white void, or as in the case of lagendarylugia on a solid color field. In your work the parts that are not the main focus are just as important as the subject you are illustrating. While it's simple to get excited about drawing a cool Pokemon and just rush it out there for the internet to look at, take a bit to really make it from a typical "lookie what I did" drawing to a "damn that's awesome" piece of art. Perhaps MegaSceptile is stalking through some undergrowth or tracking prey (assuming hes omnivorous). Set a scene, tell a story, set a mood...it doesn't take too much more effort.
Renosaur: Yep that's a Muk. More than one shade of gray would be welcome, but I'm not really sure what you were going for. Maybe it's fine how it is.
V0x: Cropping. It's a thing. I take it that you are practicing drawing characters in the modern Disney style and you are just starting out with digital coloring techniques. Good start, but even when it's a practice sketch/study you should put thought into the cropping. I know I'm a little nit picky, but why does the hair extend lower than where the neck cut off? If the hair goes lower, so too should the figure. Perhaps add the top of the dress/shirt or extend to the full figure. Don't be afraid to draw bodies. Drawing a good head is worthless if you can't draw the rest of a person. On a brighter note, I like the color palette and the attempt at adding hair highlights and lowlights. Perhaps try out some brushes in the program you use. Photoshop and Painter have cool options. You can google hair tutorials that turn out to be quite easy to get the hang of.
lagendarylugia: Good idea with the pose. Rather catlike. Not too reptilian. Most large reptiles are low to the ground and very sturdy looking, but this agile pose fits Sceptile well. If you don't have one, pick up a French Curve. You can use it to make the long swooping lines, such as his back and tail, more consistent and have them move more fluidly as one. It's a good idea to find the flow of motion in a piece or a figure and in this case it's wavy, like an S. I wish the abrupt downturn of his back would have been echoed with an abrupt upturn of the tail though. Here it looks like a sharp, aggressive line for the back, but the tail is this calm, soft curve. Also, good start with using color holds on the line work. It is a bit inconsistent though as some areas that were made dark green (the leaves on his elbows) while other areas that are the same thing were left black (leaves on the shoulder and tail). I'm also not too sure about the black outline around the whole thing. Keeping color holds on lines consistent and clear to understand really separates novices from pros, and you are right there on the edge.
To all three, keep making art and keep sharing it with people. Sorry if I am wordy, I majored in Fine Art and endless hours of critique does that to you :)