The penultimate episode of Young Justice season 4 featured a major character death that almost closed the classic DC Comics storyline Infinite Crisis.
The final story arc of Young Justice season 4 seemingly borrowed from the original ending of Infinite Crisis. The first Robin Dick Grayson had originally been slated to die a heroic death to save the universe leading to a renewed partnership between the then estranged Superman and Batman. Unfortunately the death of Dick Grayson in Young Justice while heroic did not yield any obvious benefit to make his sacrifice worth the cost of killing off one of DC Comics most important heroes.
The events of Young Justice season 4 episode 25 Over and Out placed Nightwing amid a group of young heroes who took up the task of guarding a portal leading out of the Phantom Zone. As his allies held the pass Nightwing went through the portal and emerged into Supermans Fortress of Solitude where General Zod and his wife Ursa were using a special solar array to speed their absorption of yellow sunlight and boost their strength. Nightwing attempted to destroy the super sunbed but he was crushed to death after LorZod General Zods son collapsed the statue of Supermans parents that Nightwing had been using as cover.
Curiously Nightwing almost died in a different version of the Fortress of Solitude in the finale of the 2005 comic book miniseries Infinite Crisis. A followup to the original Crisis on Infinite Earths Infinite Crisis restored the idea of the DC Comics multiverse and was meant to usher in a new era of optimism following what is commonly known as the Dark Age of Comics. Opinions differ on how successful Infinite Crisis was in this particularly given how many heroes were needlessly killed during the event. Not to mention the fact that Nightwing was originally planned to be one of them. Despite this the storyline is still generally wellregarded today.
The finale of Infinite Crisis teamed Nightwing and the Conner Kent Superboy up in a raid upon the ruins of the Fortress of Solitude which had been taken over by SuperboyPrime. The original plan would have seen Nightwing die purely because his death would have had the greatest impact on the largest number of characters. However writer Geoff Johns persuaded CoPublisher Dan Didio that it would have more resonance for Conner Kent to sacrifice himself in Dick Graysons place proving himself to be everything the twisted SuperboyPrime was not.
It does not seem to be a coincidence that the buildup to the finale of Young Justice season 4 also features Conner Kent and Dick Grayson so prominently like Infinite Crisis. However the endgame here is far less obvious as Nightwing seemingly died for nothing. Fans hopes are high however that there may be some sort of payoff perhaps borrowing from the reality of Injustice where Nightwing died and returned as Deadwing inheriting the mantle and powers of Deadman.