Time to practice some more.
Various things are wrong with this anatomically-wise. But that seems to be a common trait in your drawings, except the Iron-man one. The main flaws are the short/small arms, long legs, weird torso, etc. etc. The background isn't particularly good either. I don't really like it either, so that's probably why I am sounding so harsh in this review. Just practice and study more, you're getting there.