At best, The Sandman’s Morpheus is an apathetic member of the Endless who leaves everyone to their own fates while operating as king over his realm; at worst, Morpheus is a vindictive bringer of cruelty and despair the likes of which his mortal targets could never even fathom–and while Dream was shown as the protagonist of his own story, there was one instance in DC continuity where he proved himself to be a Justice League-level threat.
The Sandman by Neil Gaiman and Sam Kieth details the life of Morpheus following his capture by the hands of Roderick Burgess–an amateurish sorcerer who ensnared Dream while trying to capture Death. Upon Morpheus’ capture, Burgess stole from him a number of artifacts that contained his power: Dream’s bag of sand, his helm, and his ruby which is known as the Dreamstone or Materioptikon (sometimes spelled Materiopticon). Morpheus was held captive for 70 years, and during that time, his ruby traded hands with no fewer than three people: Ruthven Sykes, Ethel Cripps, and John Dee aka Doctor Destiny.
In Justice League of America #19 by Gardner Fox and Mike Sekowsky, the JLA are being attacked by their villainous doppelgangers who seemingly came out of nowhere. Not only that, but these evil copies of the world’s greatest heroes are giving the Justice League a bad name by committing crimes and causing mayhem. In the end, the Justice League figures out that the villain behind this scheme is none other than Doctor Destiny who was using the Materioptikon to create the evil Justice League, a team John referred to as the Dream Beings. After tracing this act of villainy to its source, the Justice League are able to stop Doctor Destiny and set everything right with the world. However, the damage Destiny caused with the Dreamstone was extensive and nearly put an end to the Justice League forever.
Doctor Destiny is Nothing Compared to the Sandman
While it wasn’t the Sandman himself who wielded the power of the Dreamstone against the Justice League, it was Dream’s power that was being wielded against the team of super friends–and by a mere human nonetheless. By using the power of the ruby–which grants the user the ability to make whatever they dream come true–Doctor Destiny was able to dream his own Justice League, one that was strong enough to beat the original team, both in terms of defeating them in combat and ruining their reputation.
If someone like John Dee could use the power of the Materioptikon so effectively against a team of heroes who have literally battled world-ending aliens and cosmic gods, imagine what a member of the Endless could do with that power against them. Thankfully, the Justice League have never done anything to invoke Dream’s wrath, so they are positioned comfortably on the apathetic end of Dream’s aforementioned ‘mortal involvement spectrum’. However, since Dream’s power was enough to bring the Justice League to their knees when he wasn’t even the one wielding that power, DC confirms that the Sandman is secretly a Justice League-level threat.