these sketches have great line quality! i like them a lot, but something is off about the frog. you already mentioned the perspective problems on the horns of teh creature, so i will stay away from that one. i feel that the frog "floats" a little bit. possibly due to minor perspective issues, or the lack of the left hind leg, it does not seem to rest solidly on the ground. posible this coild be solved by throwing in some grass or a hint of a surface on which he is sitting... who knows.
by the way, it is nice to see a drawing that is not steampunk or fantasy on CA. quite refreshing. what sort of reference did you work from? frogs don't really like to sit all that still....
Damn... that's why I posted, I never realized the perspective problem in the frogs front legs until you mentioned it. I don't use references when I do stuff like this, I've drawn a few frogs before so I just went from memory and played with the proportions.
Really great sketches dude. You've got nice ideas. Nice "swooshy" line very fluid and all. And although your style is cartoonish you have nice feel of anatomy - myscle shapes etc. The horned guy is my favourite.
The chopper guy is way cool, and I have NO room to talk when it comes to mechanical stuff, but the front wheel along with the struts(?) and spokes feels a little disconnected. I know it's just a sketch (and a nice one at that) but it's about the only thing I could offer any actual criticism on to balance out my adoration of the frogs.