The blog Chocolate Hammer mocked this trend with the game Darker and Edgier, in which familiar franchises were warped beyond recognition and readers had to guess what they originally were. The posts in question can be found here and here.
Suburban Knights compared to Kickassia. While both are hilarious and Kickassia indeed showed off Critic's lack of sanity well, SK had a really dark villain that made the mood drop in whatever scene he was in, innocents getting blown up, a Bittersweet Ending where Critic hopes to find the Necronomicon in order to revive Ma-Ti, death not being at all cheap and actual, honest-to-God Tear Jerkers.
In a more meta sense, The Nostalgia Critic both in-character and out-of-character openly hates this trope when done poorly and, as he puts it, is "dark for the sake of being dark" instead of being dark to convey some message or have some purpose. It comes up in a good amount of reviews. Ironically, his show has got darker too, with Critic having... issues, Santa Christ Took a Level in Jerkass, a lot more Nightmare Fuel and Doug confirming that he's turned Critic's endearing Christmas love into psychosis.
The Super Carlin Brothers have a series called "Rated R Pixar," where the plot of a normally G or PG rated Pixar movie is retold in a very dark manner.
When compared to the movies, The Gungan Council is definitely more mature across the board. However, whether or not it beats out Legacy depends on the writer and character.
"Zest Online Riddle" is a game similar to NotPron, and it's... weird. It also has dark, oppressive music and, overall, it's... creepy. Thing is, unlike most online riddles, this actually has some kind of a story to it, and from what this troper knows, it appears to be darkening "The Wizard of OZ", among other things.
Parodied by The Onion, with this (fake) story about a cereal mascot getting a dark backstory.
For Yu-Gi-Oh! The Abridged Series, compare Yu-Gi-Oh: The Abridged Movie and Yu-Gi-Oh: Tenth Anniversary Abridged Movie. While both are still quite funny, the latter has a greater amount of violence, more blue jokes (courtesy of Jaden), and an actual Tear Jerker with the retention of the death of Yugi's grandfather.
Board James started off as a Lighter and Fluffier spin-off of the Angry Video Game Nerd, at least until the "Dream Phone" episode. After the series went into hiatus for a couple of years while James Rolfe worked on the Angry Video Game Nerd: The Movie, Board James returned to the eponymous character alone, with Motherfucker Mike and Bad Luck Bootsy nowhere to be found and an overarching story arc about James's Sanity Slippage and whether he killed his friends if they even existed to begin with...
A bit of an overlap with the Advertising section, but someone created this◊. Extremely dark, gritty, and honestly depressing, until you get near the end... OOOOOH YEAH!
While the original Ghost_K (Order of the Guardians) setting is a standard Alien Invasion Sci-Fi story with elemental heroes fighting them, it has spawned a much bleaker prequel series in the form of K21 Sqaured. Here the enemies are entirely human, with an array of disturbing goals. Elemental power is abused more readily as it not seen as a blessing like it is in Order of the Guardians storyline.
The collection of short stories that compromise the Subterfuge Chronicles and Shattered Endeavours manage to be Darker and Edgier than even the main K21 Squared storyline, with the majority of the stories set from the perspective of antagonists. Tarnished Perceptions also manages this, but is arguably more in line with the way in which the main story is portrayed.
Second Great Battle of Siberia is this to the main Ghost_K setting, as it provides a more futile depiction of the efforts of humanity to defeat the aliens with all of the main characters managing to die in the process.
Raymond Sipe has a song about Cthulhu that pretty much does justice to its source. However, when you compare it to songs about forum places like /v/, /mu/, and even /mlp/, as well as many of his other songs he's done, and it makes its darker and edgier motif all the more surprising to see.
Before its first, and original cancellation, Ben's Rants were very tame. The worst that Benthelooney would put in was alternatives for curse words. However, when he uncancelled his rants in 2012, Ben Tannehill started writing in more personality for the character, and made him more cartoony, causing for the newly produced rants to include references to violence, and occassionally, sex. Whilst these aren't as bad as some, it is still raunchier than anything that Ben did, before the rants were resurrected.
Not only that, but in the credits of Ben Rants: Sanjay and Craig, the song has an uncensored swear word. Ben stated that the reason for not censoring it was because he refused to censor such an awesome song.
TV Tropes: Darth Wiki is where all the negative opinions go to. And a couple of other dark stuff.
Dragon Ball Z Abridged, while still being mostly comedic, seems to be diving into this with the Cell Saga, specifically around the time when the Big Bad himself is introduced. The fact that Cell's presence is, unlike all the other villains who appeared in the series prior, actually treated with complete seriousness by the cast should be a sign of things to come.
The Worst Muse has commented on this multiple times.
Don't you think it's time for a gritty live-action reboot? Like Wolverine, but grittier. Make it grittier.
A Giant Sucking Sound, the election of Ross Perot results in a more chaotic 1990s. The constant violence and the murder of prominent people in entertainment like Steven Spielberg and Harvey Weinstein causes this effect in popular culture In-universe.
The Tech Adventures storyline in the Brave New World Universe is notorious for being Darker and Edgier than any other story in the series by a long shot. Where the original Brave New World storyline occasionally had characters seriously injured, Sasha was at the brink of death so many times that the other writers on the project lost count. It culminated in a Bittersweet Ending when Shasha sacrificed himself to save the rest of the Chosen in Joanna's secret base.
Season 2 of The Music Video Show. While the first season was lighthearted, the second season sees the host of the show slowly delving into Sanity Slippage. Throw in attempted suicides, a mental breakdown, a book with a creepy hand coming out of the front cover that is possibly a spell book and harsh jokes to boot. There's also the fact that Fluttershy is not real, Dylan says that he's the Devil and takes Pinkie Pie with him in episode 50 after revealing that the host killed his parents. Holy shit.
Mortal Kombat: Rebirth by Kevin Tancharoen gives a noir look to Mortal Kombat, eliminating the campy aspects from most depictions.
Joseph Kahn's Power/Rangers does this for the Power Rangers Zordon Era. It's actually a Stealth Parody of this trope, with the ultimate message being that no matter how much fanbases may like the idea of giving lighthearted kids' shows grim-n-gritty reboots, ramping up the violence, sex, and dirty language (even if it doesn't come across as forced) will not make the comical elements go away - if anything, it just throws them into sharper relief.