The Injustice 2 added the Teenage Mutant Ninja Turtles in Fighter Pack 3 (released in 2018). Instead of being four separate characters, they were one playable slot with a unique mechanic:
Leonardo 🗡️ — balanced, uses dual swords
Raphael 🐢 — aggressive, uses sai
Donatello 🔧 — range-focused, uses bo staff
Michelangelo 🍕 — fast and flashy, uses nunchaku
The cool part is that you could switch between the four brothers depending on the gear/stance setup. They also had their own intro animations, dialogue, and interactions with characters like Batman, Superman, and The Flash.
Their addition was a big surprise because Injustice is mostly DC characters, so having cartoon mutant turtles fighting gods and superheroes was pretty wild.