Basic Trope: A light work is either retooled or re-imagined to be darker than it previously was.
Straight: A cartoon is a fairly lighthearted action cartoon. A few years later, it's retooled into something different which is far more edgy in terms of subject matter.
The original cartoon is explicitly for children and is on the level of Teletubbies. The retool makes it a 18+ gorefest set in a Wretched Hive with genocide-scale violence and every other word being a swear.
The writers ran out of ideas with the show as it currently was - the retool will allow them to explore new stories, as well as some implications that were left unsaid.
Lampshaded: One of the characters remarks: "Wow, this place is a whole lot scarier than I remember..."
Invoked: Emperor Evulz deciedes to begin his conquest, and things start to get darker.
Defied: The Heroes train harder to prevent villians from taking over.
Discussed: "Remember when all we did was stand around and tell jokes?"
Conversed: "Ah please, that show's for kids. I mean, look, that...one guy is killing that other guy. And did he just swear?"
The darker and edgier aspects only affect the parts of the show which were prone to dark edginess to begin with, while the lighter and softer elements simply become stronger from living side by side with the darker parts of the story.
A meta example: People are attracted to the darker edgier version because they think there will be conflict, tragedy, and drama; but once they see it, it turns out there are no meaningful conflicts and nothing is portrayed dramatic/tragic or anything. They just made it darker because they it would be "kewler" and rake in a lot of cash.