Extermination

"We just went through another extermination. We lost so many souls and it breaks my heart to see my people being slaughtered every year. No one is even given a chance! I can't stand idly by while the place I live is subjected to such violence!"

- Charlie Morningstar, about The Extermination

The Extermination is a bi-annual, formerly annual, purging event wherein Exorcists from Heaven, armed with angelic weapons, are sent down to Hell to cull the overpopulation by eliminating as many Sinners as possible.

In "Welcome to Heaven", it is revealed that the idea was originally pitched by Adam himself to Sera which convinced her it would prevent the possible uprising of the demons.

Description
The extermination takes place in the Pride Ring, targeting only Sinners, while Hellborn species (and Charlie) are spared from the Extermination due to a pardon from Heaven that Lucifer managed to obtain. This also permitted that the other six Rings of Hell are left untouched from Exorcists, since Sinners are confined to the Pride Ring.

Adam was the one who conceived the plan, and Sera (whom feared an uprising of Sinners from Hell would threaten Heaven) eventually agreed to it as long as the rest of their people was kept away from the truth. A rule was also provided to some of the Seraphim that no angel except Exorcists must know about the Extermination.

Despite authorizing the Extermination, Sera herself plays no part in managing or handling it or anything related it, leaving everything to the leaders of the Exorcists, Adam and Lute. Due to this, the duo have free reign to do what they please in relation to it, such as handling Charlie's attempts to prove that Sinners can be reformed.

It is possible to avoid being killed in the Extermination, since in the Hazbin Hotel pilot many demons, such as Overlords and demonic royalty, took shelter in various buildings in Pentagram City. However, it is unknown if the Exorcists will attack inside buildings.

The end of the Extermination is signaled with an audible gong of the Clock Tower. Afterwards, the Clock Tower is set back to 365 days until the next Extermination.

History
When the population and power of Hell grew, the Angels of Heaven created an annual purge called The Extermination as a way to prevent Hell's forces from uprising. This was eventually converted into an "overpopulation managing" event.

In "Overture", Adam decided to move the next Extermination to be in 6 months to prevent any rebellion or uprising from Hell after they discover that an Exorcist was killed. The Clock Tower changed to 176 days to reflect the new Extermination date and the news of the new date caused great panic in Pentagram City, and possibly in all of Pride itself.

In "Welcome to Heaven", Adam accidentally reveals to the Heavenly Court about the extermination, which was previously unknown to all of them except the exorcists and Sera.

Trivia

 * One of the games at the Loo Loo Land amusement park is based on the annual event, with faces of the Exorcists displayed on the booth.
 * Faustisse believes that Lucifer may be assisting in the coordination of the exterminations.
 * As implied by Lute in "Overture", Lucifer himself works together with the Exorcists and Heaven in regards to the Extermination. With Lute stating that he had at some point somehow arranged a "pardon" for Charlie and the other Hellborn demons, making it so that Exorcists are only allowed to kill Sinners per Heaven's agreement with him.
 * As revealed in "Dad Beat Dad", Lucifer actually despises the Sinners of Hell and thinks that Sinners are "violent, destructive psychopaths, hellbent on causing as much pain and destruction as possible". Lucifer himself considers them all "the worst" as they were given free will and did terrible things with it, and as a result, he does not believe it is possible for them to be redeemed.
 * This would explain why he only fought to get a pardon for all the other Hellborn residents of Hell from being targeted during the extermination as well as to why it is forbidden for sinners to freely travel to the other rings of Hell.