Some details in the Abandoned by Disney series are perceived as unclear or confusing, and so theories on Abandoned by Disney exist, conclusions backed up by interpreted evidence.
The yellow fluid is vomit
This theory suggests that, based on the evidence from A Few Suggestions, the yellow fluid that originally spewed from Photo-Negative Mickey's neck in Abandoned by Disney is vomit.
The photo-negative of yellow is blue. It is clear that a human died while wearing the Photo-Negative Mickey suit. This human may have bled out. However, there is no such thing as blue human blood. If the yellow fluid is actually vomit, then this theory would explain why the fluid is so chunky and why there's so much of it.
The yellow fluid is photo-negative water
This theory suggests that, since an employee obviously died inside the Mickey suit, said employee may have died by drowning, and that the aforementioned yellow fluid may actually be photo-negative water.
The photo-negative of yellow is blue. However, there is no such thing as blue human blood. If the yellow fluid is actually photo-negative water, then it would explain the yellow fluid's unnatural color. This theory however does not explain the yellow fluid's chunky texture as described in Abandoned by Disney.