It was just rectal bleeding mixed with anal mucous.
In this thread I was worried that I was anally graped in my sleep because I had jelly dripping from my butt in the morning. But the purple monster who’s staying with us now is a nurse and he told me that it’s just anal mucous that got mixed with blood from my rectum. It then got darkened slightly by residual feces and looked just like purple grape jelly. Well, that’s a relief. I’m so glad I wasn’t graped.