Crossbones

Crossbones is one of two Civil War villains whose identities have been revealed, and he is, basically, just an enforcer. Like Sharon Carter, he has no superpowers "“ however, he proved himself against the Falcon, who only escaped because the building they were in collapsed.

After the events of Winter Soldier, Crossbones is back, and he could be the reason for the entire Civil War. So yes "“ he is dangerous. However, the fact that he has no superpowers and that he is beaten by even the Black Widow (as some of the official pics have shown) tells us that he doesn't deserve a higher place on this list.

However, he is infamously known by comic book readers for the role he played in Captain America's death "“ so he has that, at least.