ok so like.
hypothetically
if somebody had a crossover fanfic idea that centered mostly on just two fandoms, but that used the fact that both fandoms have had multiverse shenanigans before to borrow a few things from adjacent fandoms (say, having a version of one of the TMNT snagging something from a different TMNT iteration as the multiverse-hopping thingy they're in flies by) that then became crucial to the plot, but didn't have the characters actually venture into those other fandoms directly, how would you tag that











