Hmm. Well, when they're random doodles, I don't feel that there's much I can offer in the way of constructive criticism. XD; Though it does look like the eyes may be slightly too close together. ^^; I think they're supposed to be far enough apart that you can fit another eye in between. XD;
I love the characters, especially the one with markings and wings, as I mentioned. ^^ I think I have a mini-obsession with wings. ^^; And I love how the sunglasses turned out on the one that's your favorite. The ponytail looks great, too. I love how you draw hair.
Boredom can be a fun thing right? I love all the different characters and the different expressions. Keep it up! ^_^