These are great for a first attempt. This, perhaps, has to be my favorite:
It's just so pretty -- no offense, I'm not saying it's girly -- but the flames look kind of wrong to me. The little flame on the tail is probably my least favorite part of this sprite, but it's still beautiful.
I've never done anything from scratch, honestly, but after seeing these, I think I'll try it. The bird, unfortunately, was my least favorite. It just sort of looks awkward, you know? Maybe a little tweaking could help.
The grim reaper looks kind of cool, though. Like Reck said, the leaf on his scythe is drawing attention. You could try shading it a little bit, or add something to make it blend with the whole picture.
The blow fish is magnificently made. Pure talent shows through you. The spikes are a little weird though, but it still doesn't change the fact that I love this sprite.
The lion, at first glance, is awesome. But when you look at it a little closer, the head of the lion is a little out of place. It looks awkward for some reason. Maybe it's the mouth, the teeth or I don't know, but it just looks weird.
But after all that, it's great! Don't know if I helped you much, but you certainly are talented. I'll try and follow in your footsteps, if it's even possible for me to do that. It's awesome, just do what you do, and maybe take tips from other people, and you'll make some of the best sprites ever imaginable. Good luck~ :)