10 Justice League Villains MORE Powerful Than Darkseid
5. Doctor Destiny
Doctor Destiny's backstory changed somewhat pre and post-crisis, but in all versions his powers revolve around dreams, control, and specifically a gem called the Materioptikon.
He's probably best known to comic readers from the '24 Hours' issue of Neil Gaiman's Sandman series, wherein he remains in a diner for 24 hours, controlling and manipulating the patrons through the use of the Materioptikon.
In this continuity, the gem is one of Dream's three artifacts of power he needs to return to full strength, but during his imprisonment it fell into the hands of John Dee. Dee becomes Doctor Destiny by using the Materioptikon, even overusing it to the point where he becomes emaciated and skeletal in appearance.
While not appearing a great deal since The Sandman series, he has been shown to be a credible threat to the League, as in a JLA Annual, he manages to turn people's dreams against the heroes, eventually capturing them all before being thwarted by Elongated Man and Zatanna.