General Zod Conquers Earth
One of the biggest moments of the finale is when Superman's cape suddenly changes from red to black. The 'S' symbol is replaced with the emblem of the House of Zod. This development cements the changes to the timeline caused by Brainiac's defeat. Superman's entire legacy has been undone in a single moment.
In our first glimpse of Earth, we're shown a troubling look at an American city as all of its citizens are frozen in place, unable to move. The scene resembles the fates of other planets that have been added to Brainiac's collection. This could mean that Brainiac will eventually be freed from the Phantom Zone. If that happens, Brainiac will presumably continue collecting civilizations in his journeys across the universe.
In the same scene on Earth, we're given a look at a statue of Zod, which indicates that Earth is one of the many planets Krypton will conquer under Zod's rule. One way to interpret this scene is that Zod will take Earth first, and in the years to come, will be unable to stop Brainiac from taking it for himself. Either Zod fails to defeat him, or is too busy conquering other planets to stop him. What we can gather from this scene is that the rise of Zod is just as bad for the universe as Brainiac.
When Zod first revealed Brainiac's true plans to Seg and the others, he explained that the only way to defeat Brainiac was to unleash an "unkillable" weapon: Doomsday. The fan-favorite villain, who bears a remarkable resemblance to his comic book counterpart, has been guarded by a group of cultists for centuries. Thanks to Adam Strange, Zod was unable to set Doomsday free. He made a second attempt in last week's episode but was thwarted by Seg's efforts to hide Doomsday from him.
Just when it appeared that Krypton would be spared from Doomsday's destructive fury, the creature smashed his way free of his prison in the closing seconds of the season finale. Doomsday finally breaking free of his prison was an important moment that the series had been teasing for several episodes.
Doomsday's freedom could have catastrophic consequences for Krypton. This could be particularly troubling for Zod, who will be expected to maintain order. If Zod can't contain Doomsday, the general's reign may come to a quick end in season 2.