This story is a sequel to I believe your wife is a vampire!
The other crusaders have gotten their cutie marks, leaving Sweetie Belle a lone blank flank. But then she learns about a pony, who sold his soul to tartarus for his cutie mark. So, a dark moonlit night she's walking down to the crossroad, but to her surprice, she's not alone...
A follow-up, rather than a actual sequel. Unedited.
Oh, and by the way, you might say it's a crossover.