The mirror-universe Quark runs a bar on Terok Nor and secretly helps Terran slaves escape from the station, a kindness for which the Intendant has him arrested and put to death.
In the mirror universe Quark still keeps a bar on the station, but his character is almost the reverse of the profit-minded Ferengi of the prime universe. He quietly uses his business to smuggle Terran workers off Terok Nor, apparently without expectation of reward.
He appears in Crossover, where the prime-universe Kira approaches him in the hope of obtaining a transporter to get home. Before he can help, Garak arrests him for aiding escaped slaves.
The Intendant professes regret but orders his execution all the same, asking that his death be made quick. His fate is one of the first signs that the Ferengi of the mirror universe tend to come to a bad end.