I've noticed that a lot of these crossover ideas seem to take the form of artificially inserting a character from one universe into another. But what about the idea of actually blending two universes together so that all of the characters on both sides can coexist and interact within the same reality?

I make this distinction because my story does that. So from every character's perspective, all the events in both origin stories have taken place in the same reality. I find this to be a pretty compelling way to create this universe because it feels natural and makes both origin stories flow together as if they were all part of the continuous story.

I wonder how common it is to do something like this.

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Doing such a thing outside of alternate Equestria's would be quite a feat in and of itself, mainly because doing so would more often then not mean needing to make some way that some sentient creature other then ponies were involved, which would in turn mean throwing most things out the window.

But like 3964466 said, there's always retelling, taking events from another world and transplanting them into the FoE universe.

Personally, this is my favorite way of doing things, since you can almost always make it work out pretty well if you think things through enough (and trust me, read any of the baselines I've done, I always think through the blending).

3964543

Well for my particular story, I found that it blended very well because (a) both origin universes are MLP fics, and (b) their primary events take place in entirely different times. Fo:E happens to be the perfect setting for Nyx to complete her character arc too. It helps that these stories both share so many characters. There are very few direct contradictions, if any. I think the only one I really spotted was that Twilight's mother is named Star Sparkle in Fo:E where she's Twilight Velvet in Past Sins.

What I've found really cool though, is the fun blended moments like when I made Spell Nexus the inventor of the megaspells, working for Fluttershy at the Ministry of Peace. It works so well, I can hardly believe it. Spell Nexus of course, being the pony who invented the spell which created Nyx. The pony who is wracked with guilt over his role in the whole Nightmare Moon debacle, and felt his calling is now to create healing spells (which was the original intent of the megaspell). Stuff like that I find very satisfying.

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I'm working, mentally, on a fic that sticks FO:E and City of Heroes in a blender and hits puree.

I say mentally because it's reliant on giving a Fallout style outcome to a crossover fic I'm already writing for City of Heroes.