My Little Pony XIX: I Emptied Your Thread

[Kindablue]

For sake of my continuity, they still have the necklaces; the necklaces, having their cutie marks, are bonded to them and only them. The necklaces let them access the Rainbow of Light, as long as Twilight Sparkle is there to provide the spark of magic.

Are they like Slayers, in that there's one group every generation (or one group for every generation that needs them)?