Before the Hasbro/Kenner conglomerate purchased rival toymaker Galoob, they attempted to compete with Galoob’s MicroMachines via their own series of miniature figures, vehicles and playsets, collectively known as MicroVerse. Since Kenner held the Batman license at the time, they produced a few MicroVerse sets related to Batman: The Animated Series / The Adventures of Batman and Robin, including this tiny rogues gallery pack. Each figurine is roughly the size of a fingertip.
Personal photo taken in 2005, though I think the set itself was released concurrently with the show. Also: KB Toys “clearance” sticker!