@raw19
 
In context, Spike’s had that necklace since between Season 4 and 5 in the Genie Twi version of events (That in most cases don’t differ too much from the canon show) where through a dramatic turn of events Spike creates whats called a Dragon’s tear during a rather dangerous encounter (This same event being where Spike got his scar/purple eye) on a return trip to Saddle Arabia with him, Twilight, and the others in the Mane 6. They just recently discovered a new ability of the gem in a new story that finished in February this year that follows sometime after The Ending of the End. That it can summon Spirits of the Deceased as long as anypony who was either blood related or friends with them when they were alive. Which is why Pear Butter and Bright Mac are here as spirits.
 
The Dragon Tears in I Dream of Twilight Sparkle/Ask Genie Twilight are a central part of the lore. Though it’d definitely take too much in just one comment to mention everything. But I’ll at least put the gist of it that’s relevant to the current pic.

Spike’s necklace?