Hello there Zero.
I'm only going to comment about your latest updates, more precisely the Madness combat sprites and the Hinden-Peter.
Hinden-Peter;
I can see that you're one of the more advanced spriters on here, although I see that there are a few problems in the shading you used for the blimp parts. You used normal shading for the 'rubber' of the blimp (I believe it is that, correct me if I'm wrong), as is normally used for smaller sprites. On a small sprite (around the size of your madness sprites), there wouldn't be a problem. Except here, you make the blimp look as if it has very little balloony surface, if you get what I mean.
For instance, go
HERE. It isn't the best of reference images, but I believe it illustrates my point. As you can see, the shading 'reaches' around the balloon a lot more than what you represented. For what you did, it'd make me believe that the rubber of the blimp goes flat-curve-line-curve-flat, whilst it should represent bounce-line-bounce-line etc. My tip for this is, well - don't be afraid of the darkness of shading. Sure, larger sprites demand more work on the choice of color, and the way you use it. Try to use more shading.
I guess the same'd go for the Peter head, if it is made of the same material. Although if you want to keep that cartoony, go ahead.
Madness sprites;
Smaller sprites are good, indeed, as you can have a good view d'ensemble whilst still zooming in. Although there are a few things that bugged me in your sprites. If you're attempting to do the sprites using the actual game as a reference, go
HERE.
As you can see, there is no 'lighter' shading after the darker shading, so the light line is unnecessary, although is useful to give the characters more depth, I give you that.
For the cross on their head, the tip of the cross is pointing a bit too much inwards, as if you were following the outline of the head (the cloesest outline in order to 'aim' the cross. I'd wager that the head would look much more circular if you attempted the crosses as they are on the image, which follow a certain perspective to the spherical head. Since I believe you draw at least a little, look at how people normally draw heads - a circle, and then a cross over it to show where theface is situated. This should illustrate what I mean.
I like the colors you added to the sprites, even though I believe the game itself only has red-like colors (I absolutely love that green. Keep using it, in my opinion). I also believe you made the hands look realistic, which is a great job on your part, as realistic hands are hard to do - although that bottom-left pixel on the right guy's right hand bothers me. perhaps just a darker shading? I don't know.
Anyways, great work, Zero. I hope to see more of yours again.