The Alexandria safe zone was invaded by a zombie horde, then it would be not surprising if history repeated itself. So I suppose that the temporary relief that Rick the survivors will have in Alexandria is a spoiler, and there have been some others that are mostly rumors, based on what we know from the storyline in the graphic novel series.
For example, we know that Glenn (Stephen Yeun) is going to die at the hands of a villainous man named of Negan, as this is what the graphic novel series has shown in black-and-white (literally, because the comic book source material is in black and white).
It is unknown whether Glenn will die in Season 6, and if he will die at the hands of Negan, who has yet to make an appearance on the television show.
Negan brutally kills Glenn. If he actually does feature in season 6, Glenn could be one of the major characters who get killed next. Robert Kirkman
Oh, and another thing could be more zombies. The show has lately focused on humans as the main villains, but Season 6 might remind us why Rick and his gang are together in the first place.
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