As life in Equestria goes on, Comet Trails realises that he doesn't have any money, or at least no bits. He sets up shop as a spellwriter, with Spike the Dragon working for him as a part-time badge inscriber. Their work is only popular with Unicorns since they're the only ones who can use the spells, so they devise a way of allowing other races to use them.
Of course, not everything goes swimmingly.