Mirthful has been dead for over a millennium, but a pony with his kind of power and influence never really goes away. Most notably, his legacy lives on through the Gigglemancy cult founded by his most loyal apprentices in life: Troupe of Mirthful. Taking their dress code and mannerisms from him, they continue his life’s work of bringing eternal laughter to Equestria, no matter the cost. They have spent the last thousand years playing a long, subversive campaign to gather those with the talent and passion for the mission to refine their craft, and draft mad plans to fulfil their messiah’s purpose once and for all…
But in a more tangible sense, his spirit lingers on…in quite a literal sense. Just as Sombra persisted without a physical form in The Crystal Empire two-parter, Mirthful also found ways to maintain a presence on the material plane, albeit in a ghostly form. Some connections to ancient artefacts or places of significance to him have become haunts that keep him tethered, even allow him to manifest as a spectral apparition.
Many of them are even managed by Gigglemancers, for reasons that vary depending on the group. The Troupe of Mirthful themselves treat these haunts with an almost religious reverence, making them into what one might expect a shrine to a jester-god to resemble. Other shrines made around these haunts are maintained by cults that mistake his identity for some other kind of being, albeit one with great power in their forbidden art. And a rare few have been sort out by the curious and brave who came to believe the old fairy tales, hoping to bargain with the Demon of Laughter for his knowledge.
Regardless, he’s found a supply of tickle toys whose laughter has helped kept his power strong even as a spirit. Some willing supplicants, some would-be Gigglemancers who left a poor impression and many prisoners and slaves gathered by cults, offered as tribute. And on occasion, just some curious and/or hopelessly lost ponies that wandered into the wrong dark corner of Equestria…such as these two hapless stallions.
Looks like Thunderlane and Feather Bangs wandered into the wrong cave. Why did they come here? A spelunking trip? A secret mission? Finding a secret place to confess their love for each other? Took the left turn at Quarry Junction?
It matters little now, for the cave they stumbled into was one of Mirthful’s haunts, where he has manifested as a ghostly jack-in-the-box and seized them both to feed on their tickly squeals of laughter. They had better hope somepony knows where they went…otherwise they’ll be here for a loooooooooooooooooooooooooooooooooooong time to come.