Here is the design for Black Mantis in "beach chillin" clothes and "super suit" (guess which is which)
When I'm designing I'm thinking about how the character is going to move, how I can use them in shots (how their silhouette works for example), their personality, little extras in their costumes that could be used for story points, ease to draw (cutting back detail where possible), their turn arounds (Mantis' head piece thing is a challenge), strength and weight and how they are going to match or complement the other characters. There's a few other things but those are some of the main ones.
This vampire one I did shows how I designed for a 48hr animation comp. It was designed that he would float (cuts animation down incredibly), simple to draw and that the model was loose (meaning it was ok to draw it quite differently depending on the shot). His face especially was designed for large expressions
With Dash Dashing a unique focus of my design is with the characters eyes. Each character will have their own eye style. This may more suit my own animation style which is pretty close (extreme close even) to camera that I'm putting a little more detail into the face. I am however trying to make sure that the characters aren't just detailed heads on stock bodies. Doing that life drawing has helped a lot to understand how the muscles and body parts work.
So yeah 2 more main character drawings to go. Oh one last tip when doing character design, flip your drawing constantly. You do this to combat your drawing lean and you'll end up with a more solid/grounded character