In the
Disneyland forum, DLRExpert and others have reported what rides you can/can't use a Multi-Experience pass (also known as an MEP, anytime pass,
Lightning Lane - Select Experience, and by a few other terms) for. We don't have a list like that for the Florida parks, but I thought I'd report my limited experience with MEPs last week at WDW to add to the pool of knowledge.
At Epcot (January 10), I got an MEP when Remy went down. It was not good for Guardians, Frozen Ever After, and Test Track.
At Magic Kingdom (January 11), I got one for Big Thunder Mountain. It was not good for the Parade, Enchanted Tales with Belle, the meet-and-greets with Ariel, Cinderella, Mickey, or Tiana, the ILL rides (Tron and 7DMT) or the rides Jungle Cruise, Peter Pan, and Space Mountain.
FWIW, I had single park Genie+ both days. I don't think that would make a difference, but who knows. I did not test if MEP acceleration (a term used in the Disneyland forum) would work. I didn't want to risk my Remy MEP if it didn't. (I used that MEP for Remy after the ride came back up.) And I spent most of the rest of my day, after getting the MEP for BTMRR, with a friend who did not have an MEP, so we rode only rides we could both get LLs for at the same time. I wound up not using that MEP at all.
Edit: corrected dates