All right, neat but the line of action on some of these is weak. IE first guy, green robin hood ninja, at first it looked like his spine was bending inwards. So it's not just the spine that defines the line of action, the limbs support it, it all adds up to the whole.
Second one not doing a lot, third one leaning forward smooth criminal style. Last one is the best. Basically I'm suggesting you push the dynamism, make each one different.
Also all sharing the same proportions = rectangular silhouette which compounds this.
Color contrast on these is pretty bad and a lot of these colors are similar/on a mono ramp. Maybe that's part of the flat indie thing going on for some years, but push past it! You can take this further than that in that style.
Up the contrast in these 3 arenas essentially.