The Insane Cafe RP trilogy has elements of this. The first was a nonsensical, hilarious and downright Narmy. The second was more plot driven and a terrorist attack on a remote laboratory was a key plot point. The 3rd installment features several assassination attempts, a few sex scenes and an impending war. Oh yeah, profanities are uttered the second and third installments.
Cracked has commented on the "gritty reboot" trend several times.
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.
While most of the campaigns in the Global Guardians PBEM Universe were standard Bronze Age fare, the Night Life In The Big Easy campaign, which featured a solo 1980s-style vigilante facing off against a voodoo-themed criminal empire that had been built on drugs, prostitution, and white slavery, was straight out of the Dark Age.
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.
When compared to the movies, The Gungan Council is definitely more mature across the board. However, whether or not it beats out Star Wars: Legacy depends on the writer and character.
The flash series Super Mario Bros was actually much darker than the original games, as the very beginning had Mario trying to escape from something before it proceeds to a flashback: Luigi ended up killed during an ambush on Bowser's forces, Bowser successfully kidnaps Princess Peach because Mario was busy mourning for Luigi (and it is heavily implied that several of the Toads ended up killed in the assault). Bowser's plans with Peach involve using her to create mushrooms so he could effectively be immortal. After a final stand against Bowser, and successfully dethroning him, he ends up failing to save Princess Peach (resulting in her death by magma alongside Bowser), and the direct result was an eruption, getting to where the series started. Mario then faces the magma flow and essentially dies.
"Zest Online Riddle" is a game similar to Not Pron, 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.
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.