The Flash has introduced another, previously untapped corner of DC Comics into the Arrowverse - this time with a direct nod to the mythology of the Shazam character. With Barry Allen still processing The Monitor's proclamation of doom, the episode was split into multiple distinct threads. With budding mad scientist Ramsay Rosso having inadvertently created a dark matter zombie as part of his experiments, Barry had to partner with the doctor to halt the threat. All the while, the leader of Team Flash attempted to help Danielle Panabaker's now not-so-killer Frost - who was dealing with her own mortality issues in the face of the impending Crisis. Ralph Dibny, meanwhile, was forced to deal with some family matters, and Cisco Ramon teamed with Iris West-Allen to greet Earth-1's latest Harrison Wells...
Iris received word of the new iteration of the long-serving character from her intern, Allegra Garcia. Tracking him to an alleyway, Iris and Cisco discovered him in the middle of searching for something. With a gizmo on his arm drawing him to the former, she was forced to taser him and together they whisked him back to his offices. When he finally awoke, the new similarly-faced character was revealed to be Harrison "Nash" Wells, a multiverse-traveling adventurer who openly mocked The Council of Wells and felt it his mission to dispel the myths clung to by "simple-minded people". That latter quest is what brought him to Earth-1 and, despite Cisco's attempt to vibe with the newcomer, he fled back to the initial alleyway when he realized his device was only drawing false readings from Iris.
Before he departed amid a smoke bomb, however, Nash Wells revealed that what he was searching for was Eternium. Though the name only drew shrugs from Iris and the usual pop culture references from Cisco (this time to Indiana Jones and 2016's Moana), it will almost certainly mean something to fans of DC Comics. Eternium is the name for the shards that resulted when The Rock of Eternity was destroyed. The Rock of Eternity, of course, is the lair of the ancient wizard Shazam - who Billy Batson crossed paths with on one fateful day. It was also the prison for the Seven Deadly Sins. The term Eternium was coined within the world of DC by Tom McCraw, Tom Peyer, and Scott Kolins in 1998's Legion of Super-Heroes #110 (Volume 4). The resultant shards were cast far and wide across the various, infinite universes. As such, it's firmly in line with the comics that Nash Wells would have to strive so hard to find one.
The associated characters were recently seen on the big-screen in Shazam!. As such, it's unlikely that Billy Batson will be showing up any time soon. Therefore, the properties of Eternium will likely be different as a result. In the comics, the shards are akin to kryptonite, usually removing Shazam's powers. It also causes physical pain and injury to those who come into contact with it. With no Shazam character appearing in the shared television universe, the former would be pointless quality and the latter would be pretty perfunctory. Still, the implication that Shazam and that corner of the universe exist somewhere will no doubt delight fans.
It's probably safe to expect that, once Nash Wells finally has Eternium in his grasp, it will have an altogether new, potentially mystic effect. With each thread of these earlier episodes said to tie directly into the upcoming Crisis on Infinite Earths crossover, Eternium will most assuredly factor somehow. With Tom Cavanagh also set to play a version of Pariah, it stands to reason he'd be revised to be a Wells also. And could it be Eternium rather than from scientific means and The Monitor that he acquires his abilities? It would certainly make for an interesting twist - most especially in an ironic sense, with Nash Wells becoming the very thing he was aiming to disprove. Whatever the case, all will become clear as The Flash continues.