Little c/writing lurker here. I'm currently writing on a very spontaneous crossover idea between three fandoms (Supernatural, Star Wars, and Assassin's Creed). Now, I'm not aiming to publish this anywhere, it is first and foremost for me; the plot is thin at best, but I have some milestones I want to reach with my original characters as they have been somewhat stuck for a couple of years. That is why I added AssCreed, to spice it up a bit and to force my OCs to act on things they should've done something about long ago.

My question for you would be how you manage to keep the fandoms from either stealing attention from each other or one dominating the story while the other ones are just window dressing. I've written crossovers before, sometimes with more than 8 fandoms that had no business being in one story, and I feel like I have a good grip on it by now, but there is always room for improvement.

Personal experience has taught me that fewer fandoms always makes for an easier time, and having a good mix of OCs and existing characters from the involved fandoms makes it easier to keep the lore from both balanced. Maybe you have some other tips or tricks that could work. Thank you in advance!