As TheBrickBlogger has already pointed out, all of the figures from this theme are very different from a normal minifigure:
The backs of the legs on these figures are made to interface with Lego studs for seating purposes, which is probably fairly obvious. So, I am assuming that the holes with narrow gaps between them may be the focal point of the "unique shape" you mentioned. At first glance they appear to look very much like Key Hole Hangers, which suggests they may lock into/onto something.
But, after closer examination of a clearer picture, you can see that these slots provide clearance for the leg hinge assembly instead. This extra range of motion is well fitted for a theme based on "Action" scenarios. It probably provides some stress relief on the parts at the pinch point also: