Technically speaking, "Infinite Regalia" contains a wealth of information that can be used for meta on Fire Emblem's bad endings, afterlife and resurrection meta, and stuff like this. I just can't bring myself to discuss it because it's presented in a manner that jacks the Disturb-O-Meter past FE5 levels of Fucking Disturbing.
And FE5's "Deadlords" are really, really disturbing.
The text is all here
. Basically, the interaction with the Gen 1 characters is mostly funny while the interaction between the Deadlords and the Gen 2 characters is anything but, and the overall effect is more like the modern tongue-in-cheek self-aware zombie phenomenon. I don't even know where to begin applying this stuff.
Then there's the Lost Bloodlines series (the Marth vs Seliph stuff), and I don't really know where to begin with that, either. It's kind of all over the place. In some places the Einherjar show glimmers of awareness and I get the idea there's supposed to be something more to them than just puppets (Chrom and Co. also get that feeling-- it's pretty explicit). In some places they feel like one-dimensional actual cardboard figures they're purported to be (I don't like how Ethlyn's written, for a start). Some of the Einherjar feel pretty alive and, I don't know... themselves? I think the "new" characters from FE11/12 feel pretty vivid, which may be telling. They were, after all, made up out of whole cloth. Some of the Jugdrali sound more alive than others. IDK.( Good stuff and bad stuff )
Really the Einherjar are really the best weasel device in fandom. If something in the DLC bolsters your pet theory about a beloved NES/SNES character, you can point to the DLC and go "See? See? Word of God!" If you don't like their new speech quirk or personality transplant, you can wave it off with, "Eh, it's not really them-- it's an artist's rendering of the real thing."
And then, after all, this is merely canon fanfic, right? Some scriptwriting intern could've been plopped down with the 20th Anniversary Artbook and told to compile a three-to-five word description of every relevant character and then produce dialogue based on the lists. So you get a fairly bland Arthur without his moments of towering rage and this really wussy Nanna who doesn't match up to her FE4 counterpart. Not to mention an Ethlyn who apparently belongs in the kitchen. So yeah... they're artists' renderings.