Hello Trigger009. I would like to ask why do we have separate articles for most of the Injustice 2 characters? The reason I'm asking this is because, 1) this isn't the wiki for such characters, even if the TMNT are DLC characters, we have the Injustice 2 page to show this, 2) I notice that we don't always make articles for every character that appear in a crossover or psudeo-crossover with TMNT such as the characters that appear in Invasion 2, 3) Most of these pages have only one contributor. I'm not asking you to remove these articles (because I don't know if I can and I'm not taking chances) but rather, asking why do we have them.
We do have characters for every crossover. Look under the crossover characters category and you'll see many characters who have just shown up in the same work as the Turtles such as Sonic the Hedgehog, Bugs Bunny, and Spider-Man.
The only stipulation for this is that since this isn't the main Wiki for those characters, that we keep the on-wiki information to a brief background plus their involvement in the reason they're on th Wiki (ie we don't need all 79 years of Batman's history but we would a primer on who he is plus and what he did with the Turtles).
If you look at the Injustice Characters category, we have the following rule:
"Please restrict these to characters that are playable/fightable, or appear in supplement to the Turtles (such as their ending/backstory)."
So literally every character you can play as or fight against are fair game, and if like Splinter or April (or even a non-Turtles character like John Constantine) shows up in their ending, they could be added. If the Turtles are added to Injustice 2's mobile game, the characters you can play/fight in that are now elligiable, and same thing in the off chance they get added to Injustice 1's mobile game.