Oh dear, another graphical bug seems to have happened and Sunny turned back into his normal self after I regained movement. I probably should have figured out which mod was causing this back at Memory Lane.
Sunny in enough of a catatonically shut down state at this point that this probably wouldn't happen, but I personally like the idea of him using the advice Mari gave him to overcome his fears to make this final step. Deep breaths to calm down, block out the little things and focus on what's important, and keep going no matter how scary or impossible it seems. Jump.