Curse of the Crimson Throne
A student at the academy is required to undertake several dangerous steps in order to graduate, one of which is the summoning of an imp. Many students opt to take imps as familiars, but just as many fail and let those imps get loose. As a result, imps are a constant problem in Korvosa. Nests of them lurk in the eaves of the city's Shingles, often attempting to ally with or manipulate city gangs. Fortunately, the indeigenous house drake population, tiny dragons evolved from the pseudodragons who dwelled in the region before Korvosa was founded and adapted readily to the city's advent, are quite adept at keeping Korvosa's imp population under control.
Two or three times per year, the imps and drakes take flight in the skies above Korvosa to engage in mass battles. Civil unrest in Korvosa will trigger more of such events.