The Mafia's underground auction is an annual event held at the beginning of September in the Cemetery Building in Yorknew City. Usually, all the Mafia clans send their high-ranking representatives to attend the auction, and some Mafia bosses even go to the auction themselves, because it is the place where they can show off their wealth to the Mafia Community and make a name for themselves. There have been cases of Mafia clans going bankrupt due to bidding too high at the auction.
The Underground Auction that take place in 1999, the same year as the 287th Hunter Exam, is notable for being involved in a series of violent incidents:
On the night of September 1st, the Phantom Troupe attack the Cemetery Building to steal all the auction items, killing a large number of Mafia members and their clients in the process. Not knowing that the items were already removed from the vault of the building by the Owl of the Ten Shadow Beasts and are safe, the Mafia Community mobilizes a large number of members, including Kurapika and some bodyguards of the Nostrade Family, to chase after the Troupe to the Gordeau Desert.
The Mafia's superior number and conventional weapons however are no match for the battle prowess of Uvogin of the Troupe and another massacre takes place. Four of the Shadow Beasts then arrive at the battlefield and attack Uvogin together They manage to injure him but eventually are all killed by him. Kurapika then takes the opportunity when Uvogin is not on his guard to capture him using the Chain Jail. The Phantom Troupe immediately go after Kurapika and his comrades but their car is stopped on the way by the arrival of the remaining Shadow Beasts. The Troupe then kill all of them but the Owl with ease.
They quickly find where Uvogin is held captive and free him after killing Dalzollene, head bodyguard of the Nostrade Family. On the night of September 2nd, Uvogin is killed in a duel with Kurapika in the Gordeau Desert. To avenge him, the Phantom Troupe launch another attack on the Cemetery Building on the night of September 3rd, killing approximately 2,000 Mafia gangsters and a number of professional assassins hired by the Ten Mafia Dons. After the Ten Dons are killed by Illumi Zoldyck, the Phantom Troupe create fake corpses of themselves, steal all the auction items and continue the underground auction using the copies that will disappear in 24 hours.