I'm not a huge fan of the rounded rectangle balloon though..

Then check this:

nice mockup :-D

Actually, it's not just mockup, but already game, here is some screenshots (as proofs, ahaha).

u could just break up the balloon into sections like this...

Thank you for edit! I have tryed to evolve it, but still not sure that it's look right. So I just cheat by using additional lines:





Is that better?

maybe it lacks propellers to be recognized easily as such.

It's a good idea, thank you! Now I have to figure out how propellers can connect to a machine inside the airship:

I had been meaning to critique this art for quite some time, you have some nice work!
Though, your tile optimization could use some work. I had some time, waiting for a commissioner to respond, so...

You reminded me about the dilemma which I could not decide when preparing resources for a test build - make tileset convenient for leveldesign or optimize it to free up more space for tiles. Now I try to find a compromise solution based on your work, big thank you for this!

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Hehe what does the "DOOM" powerup do?

This thing blows up 5 enemies on the level.

I'm not that into NES graphics so I don't know is there any restriction on animation number of frames and timing?

I know nothing about timing limits, but number of frames is limited by the size of tileset, which is used for current level. So I have 4 frames and one of which is used for the "idle" frame.

Because your sprites are cool but I think the animation can be tweaked a bit to get rid of some of the flickery/twitching frames.
For example I love the little 4 leg mech but the legs go smoothly backward then instantly twitch back to the front.

Oh now I see it. The problem is in size of the "frame", it's 16x16 pixels and legs nowhere to swing, they rest on the edge of the frame.

I haven't read up but on closer inspection I'm not sure if its a mech or some alien creature.
Seems to have a mix of organic and mechanical forms.
I think it would probably benefit from some design decision to make it clearer what it is.
If its biomechanical then maybe use 2 separate colours to indicate that.

Yes, it's hybrid, half organic, half mechanical. It's a good idea, I will have to try it, thank you! 

It seems that his menu screen gets too gothic for a fantasy setting:



Or not?

Also, I changed GUI and some new graphics:

Very cool and moody work! But you should finish this animation. What happened after that? I think boy is teleported too. And the dog runs back into ventilation to find him on a different floor of level. Thus the animation will be loop.

Also, I think this world is not enough some robots, just edit for fun:

Impressive work!
I think walls and floor lacks contrast now. For this reason floor behind the red character is perceived as a wall:



PS: Please say this is going to be a game. :3