In Nightmares

“Mikey?”
Michelangelo doesn’t answer, standing alone in the shadows. Leonardo moves to place a hand on his shoulder but pulls his hand back when the youngest screams in utter terror, his eyes wild and staring at the space around them. It’s a sound that haunts them all to their core, ringing over and over and Mikey keeps screaming and sobbing, begging for something they can’t understand. The fungi quickly latches onto his face, mushrooms digging into his eyes, across his shell -
“Mikey!” Raph yells but Mikey doesn’t hear them, lost in his own nightmare and unable to defend himself as the mushrooms consume his face completely. Instead, they can only watch helplessly as Michelangelo gets dragged into the darkness.
~
A mysterious infestation of fungi in the sewer system of their old home causes the turtles to each become trapped in the own never-ending nightmares. Imprisoned in the dark caverns and the last one standing, Leo must battle his own fears if he stands a chance of saving his brothers before they are all consumed by their own terror.
~
TLDR: remember that 2012 episode with the fungus? I rewrote that for 2003, but much darker.