I was wondering what would be the reasons for these Mlp villains...
The Dazzlings...
Sunset Shimmer...
Queen Chrysalis...
Gilda...
Trixie...
Ahuizotl...
Suri Polomare...
Snips and Snails...
The Flim Flam Bros...
Lightning Dust...
Silver Spoon and Diamond Tiara...
Blueblood...
And King Sombra...

To become Templars in the first place?

3939963 Well, having attempted to write an Assassin's Creed/MLP fic before, I think I can help you. Templars are known for wanting to control people, for the sake of peace. They believe that under their control, people will be happy because they will not be worried. For this reason, they sought the pieces of Eden, which would give them control over people.

The easiest way to go about this is to come up with something similar. For instance, in my version, it was an ancient enchanted music box, that when played, could put the listener to sleep. When combined with the Apple (which was under Templar control) it could put the entire world/nation to sleep, allowing the Templars to control them. If you've read Naruto, just think of it like the Infinite Tsukiyomi that Madara was attempting; eternal dreams so that the world can't feel pain.

Come up with something that would give these characters reason to be Templars. It would need to be something that would make them want to gain control over the masses for the sake of peace. You may need to make it an AU fic to make it work, and that's okay.

Not sure if this helped, but if you need more, don't be afraid to tell me.

3940035 You did all you did and it was helpful.

3940049 Glad I could help. Again, if you need anymore help, don't hesitate to ask.

3940054 You got it.

Silver Spoon and Diamond Tiara are children. Put Filthy Rich in the list instead.