Midi's Sprites

[Sketchasaurus]

Ahaha, nice! I can imagine Kamekannon behaving like Bowser during his boss battle in SMB3 like that.
I like how you've interpreted the NES sprite, it's also cool how massive you've made 'im, too! I'm interested to see how you interpret and animate these fellas.
Here's a bit of artwork for additional references.

Spoiler

Even though these all have the same color scheme in the art, Titans are able to have any variety of color palettes and variations (there's even a version of Kamekannon that looks more like a Terrapin *spoiler alert) Oh, here's a bit of concept art that illustrates what I mean:

I also agree with Koopaul, the details of the backgrounds kind of interfere with the readability of the character sprites. I would consider maybe using flat colors or 2-shades for backgrounds. and a little bit more of a light blue tint to the far trees will also give it a more roomy/atmospheric feel and really add depth to the 2D world.