I always wounder what happen if a small group of the death guard showed. Could be interesting how they interact with the plague sisters. And the other ponies.

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Considering that the Death Guard are... immensely worse than the Rusted Brotherhood really could be, considering they are so far gone with Nurgle that they are borderline immortal (The Grave, being a prime example), the other Ponies would likely be in absolute terror to seeing something or someone like Typhus the Traveler.

A Word Bearer would be interesting, though I do wonder if the two guards to the temples that the CMC talked with were originally Word Bearers

Word Bearers.... i guess it would depend on who leads the host, or how fanatics are them, in this case there's no middle term, it can go really smooth, or it can literally unleash hell. Keep in mind also what kind of cultist they attract, the ones who really fit in imperal propaganda, nasty stuff. And the simple fact that IW do not trust much on them with good reasons and in this case in particular remember that Solon was already in active service when shit reached the fan at the end of the great crusade and he's not too fond of what happened

However, certain legion can feel REALLY interested in the remaining changelings...

Just imagine whom...

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Alpha Legion

Night Lords would be interesting, just to see their reactions and interactions with Luna and her guard

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Honestly... Not, really, as interesting as it could be such an interaction i really doubt the IW wouldn't let them close by some planets of distance, and with good reason

True, though when it comes to other Chaos legions, I don’t think they’d let anyone else near their planet. Hell, they’d probably try to avoid letting other Iron Warriors not associated with the company near the planet.

However, since marines who aren’t from the Iron Warriors naturally tend to be sold to them, like Dest and Serith were, such a thing could happen with marines from other legions and that’s how they could end up in Equestria

ahh i see where you're going, that's another matter completely

Interesting points, here another one that been buzzing around in my head. What about the elder? What could happen if they had a webway to Equestria? Thoughts?