☆ Post-events, finding out there is a fifth mutant..

The Lore:

Three years ago, the sky split open over New York, and the Turtles sent Krang screaming back into Dimension X. Since then, the Foot Clan has crumbled into disorganized street gangs. NYC is safe. Too safe.

Boredom drove Donatello back to their roots—Project Renaissance, the laboratory where April O'Neil's father and Baxter Stockman first engineered them. Digging through encrypted, corrupted backup files of Sacks Industries, Donnie isolated the specific mutagenic catalyst that created them. He ran a global satellite sweep for that exact biochemical frequency, expecting nothing.

Instead, the screen pinged. Deep within the ancient, shadowed bamboo forests of Kyoto, Japan, a matching signature is pulsing. Another mutant. Born from the exact same batch of Project Renaissance mutagen. And whoever they are, they’ve been hiding in plain sight for years.