Some folks have been speculating about DLC for Shredder's Revenge... suggesting alternate costumes for the characters. This mostly stems from ignorance of how 2D Sprite based games work... I have a little bit of Sprite editing experience... long before this blog came to be I did try to make sprites for various Marvel characters for the PC fighting game engine MUGEN. I wasn't a great sprite editor, because I had a SNES/PS1 port mentalitly and my animations would be choppier than editors that tried 25+ frames of animation for a standing pose. (My mentality was: "why make 25 frames if it can be done in 4 frames then reuse frames 2 and 3 in reverse to complete the cycle going back to frame 1. I'd animate 4 frames of the character standing then reuse frames 3 and 2 to return to frame 1 and complete a breathing animation.) The more fluid the animation, the more time consuming the edits will become.
That issue also covers palette swaps. Depending on how the animators coded the palettes for each character would depend if a palette swap could be doable. So "Mirage palettes" or "Toy palettes" could be something that may or may not happen.
The only true viable options for DLC would be:
New game modes, like say: Punk Frogs take Manhattan. A Story mode "side story" where the player plays as the Punk Frogs and other guest characters. This could bring new bosses and alternate levels. Like say, 3 new New York levels instead of the Dimension X levels.
Adding new characters exclusive to the Arcade Mode... like say:
Usagi (if the whole legalese with Stan Sakai can be cleared due to the so-so Netflix series)
Mondo Gecko (fights bare handed and his custom board is seen only on the skating levels.)
The Punk Frogs since they are kinda already in the game.
Ace Duck: I may not be his biggest fan, but it would be interesting to see some love for the Duck.
Since the game is in 87 continuity, Lotus Blossom Would be a possible character if Usagi is not available.
Hell, even Venus could be a doable possibility.
But going back to the Punk Frogs Take Manhattan side game mode:
The 3 new levels that replace the Dimension X levels could be:
One Central Park based level, where Scratch is the boss fight maybe retrofitting IDW's Herman to an 87 toon style as a sub-boss.
Another street level where the "B-team" ends up at Pizzaface's Pizzeria... obviously, Pizzaface is the boss battle. The pizza monsters could be reused on this level for obvious reasons.
The last "new level" could be Chinatown with Karai and Shredder's Elite acting as the boss and sub-bosses for the level.
Of course this would involve a lot of work and make the DLC a bit more on the expensove side, but it could be worth it... worse case scenario it could become a brand new side-game:
Teenage Mutant Ninja Turtles: Shredder's Revenge Gaiden: Punk Frogs take Manhattan.
As a separate game they can tweak MORE of the Base game and swap bosses. The Turtles would be unlockable, as a reward for beating the game, of course (but not Splinter, April, and Casey).
Like replacing/tweaking the first 2 levels as well, since they're more Turtle Specific.
Replacing Level 1 with a different level. Honestly. I'm drawing a bit of a blank here, since I want to avoid another street/sewer level. The only thing that came to mind was the Verrazano bridge. Mostly because I wanted to have a sole Foot Soldier hiding by being covered up with a Poncho... (it's a double reference to TMNT's and Cam Clarke's past relationship with Konami) making a full level for a Metal Gear reference is not that out there since there is a level with a Konami's The Simpsons in the main game.
Level 2 would get a name change and a different boss (Big Apple 3:45 PM) with Scumbug as the boss.
But it's not up to me... if it was, I'd make a full sequel with more extra characters. I guess we'll have to wait and see.