The following contains spoilers for Young Justice: Phantoms Episode 22, "Rescue and Search," now available to stream on HBO Max.
The New Genesis arc in Young Justice: Phantoms ended by dealing a serious blow to Lor-Zod's machinations. After a daring time heist, the young villain had successfully retrieved the Phantom Zone projector from Metron's extra-dimensional vault and was able to power it up. However, just as he was about to free his father, General Dru-Zod, from the Zone, Kid Flash and the Legion of Super-Heroes arrived to destroy the projector, ensuring the last of the Kryptonians stayed locked away for the foreseeable future. Enraged, Lor and his accomplice, Ma'alefa'ak, hijacked the Legion's bioship and ordered them to flee the scene as he plotted his next move.
One of the Legionnaires, Saturn Girl, pointed out the fact that Lor's ambitions have ultimately undone him; he had already "killed" Superboy and ensured a future where his father ruled supreme. However, Lor's plan to release his father in the present had ended with the only known projector in the universe being destroyed, ensuring the Phantom Zone prisoners would stay imprisoned forever. However, Lor seems unconcerned by this fact and instead shifts his attention to the Kaizer-Thrall, which was imprisoned by the heroes after his loss. After receiving new intel from Ma'alefa'ak, Lor sets out to retrieve the Kaizer-Thrall from the planet Oa, home base of the Green Lantern Corps.
What exactly the Kaizer-Thrall is hasn't yet been explained. It's known that the device comes from Apokolips, given to Lor and his allies by Darkseid to help them steal the projector. It's what gets them into the Mobius dimension and seems to possess an ability to Darkseid's Omega Effect, capable of torturing anyone from ordinary humans to New Gods.
"Rescue and Search" shows a brief glimpse of what's happening to the Kaizer-Thrall on Oa. During an analysis by Soranik Natu and Forager, the newest of the Green Lanterns, it's revealed that the device is not only sentient, but contains the remnants of an 11-year-old human boy. The episode ends with the Kaizer-Thrall attempting to communicate with the Lanterns, though its intentions remain unknown.
This isn't the first time Young Justice has shown humans merging with alien technology. The previous season, Outsiders, revamped the origin stories for teen heroes Halo and Cyborg, revealing that they played host to the souls of two of the Fourth World's living machines -- a Mother Box from New Genesis and a Father Box from Apokolips, respectively. The Kaizer-Thrall could be an attempt by Darkseid's forces to reverse-engineer such an asset, albeit with much darker implications. Either way, its -- or rather, his -- desire to communicate with the Green Lanterns implies that the device may not be completely loyal to his former masters.
Regardless, Lor-Zod's impending arrival on Oa to retrieve the Kaizer-Thrall remains a looming threat for the heroes. With the Lantern Corps. looking to settle the score with the Kryptonian over killing one of their own, and with Lor possibly having the Emerald Eye of Ekron hidden up his sleeve, the galaxy is in for a titanic showdown.
Young Justice: Phantoms is available to stream on HBO Max.