The last one blends into the stone because you're using the same range of values on both the character and the background. Try eliminating the brightest colour from the background, or making that colour a little darker? As I keep saying - keep the value range on the backgrounds on the low side, so that the characters can stand out against them with their wider value range.
The sword-swinging skeleton feels rather choppy, and the swing has no weight. Is it meant to? If so, have the character lean forward more as they follow through with the attack, and linger on the terminal poses longer.
