Dragon of Shadows would be Spike becoming the host of the Pony of Shadows. The idea is this:

1. Spike is the Stygian of the mane six (or Stygian is the Spike of Starswirl's group).

2. The Pony of Shadows is basically the MLPverse's Symbiote from the Marvel universe (Venom). It's powers are similar, it's relationship to it's host is similar, it's appearance is similar.

3. The PoS would act like a symbiote and look for a host with traits it would find beneficial to it.

4. Those traits would be in Spike.

Now, there are many different ways that this could go. How would the PoS attempt to bond with Spike? How willing would Spike be to bond with it? From what we saw, the PoS and Stygian seem to have a fused mind, though they can separate if the minds fight each other, so how well would the PoS and Spike work together after they bond?

Also, what would be the goal of the Dragon of Shadows (DoS)? The PoS could be:

not truly malicious, just simply animistic, trying to blot out all the light in order to create an environment more suitable to it as light is bad for it. It seems intelligent, but it still might have an animistic goal.

the same, but malicious.

Maybe because the idea was poorly executed in the first place (in the show) and the pony of shadows isn't that popular in the first place.

6643568 The thing though is that Stygian pacted with the PoS because he felt inferior to the other Pillars and felt betrayed when they mistrusted him for taking their artifacts to try and become their equal.

Unlike Stygian, Spike was (almost) always seen as an equal from the start in the eyes of the Mane 7, so there would be no real reason for Spike to be swayed by the PoS.

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He sees himself as an equal but 5 times out of 10, the Main 6 and other characters don't really view him as an equal

In School Raze Part 2, the whole exchange with Tirek, calling them, the 6 (with Spike indignantly screaming 7, and note that he's the only one saying 7) That was what clued me in

6643578 Still looks like a better batting average than what Stygian had.

Yeah true

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The exact method the PoS used to get Stygian to bond with him might not be the only means it can convince a host to bond. The PoS might just as easily prey on other insecurities it can find. It could also use the power both the host and it gain upon bonding as an allure. And while Spike has shown no interest in power for himself, he has shown to go to great lengths to help his friends. The PoS might come to him in a time of need when a great threat appeared and offered it's deal to the drake.

6643646 Now that would certainly be interesting.

6643646 I'd like to see that. And yet another reason for me to freaking FINISH WATCHING THE SHOW AFTER SEASON 6 IDHXGJF9EBC7SUSHICSJJD-

Sorry about that, I keep pushing it forwards so much it's starting to annoy, and yet I still don't go and fix this.

Let see if I can name the PoS better.

I'm The Shadows of Despair. As long as there is despair in this universe I will never go away. There is always a bit of despair in the hearts of creatures. I will hear there cries when no one listens. I will give them comfort when they'll lonely. I will grieve with them when something happens. I will give them the power they need to ensure victory.

I'm Despair. And I will ruin the happiness of others. I will make them suffer as I had suffered.