A small amorphous organism found on the Gamma Quadrant planet L-S VI in 2370, which Doctor Mora Pol hoped was related to Odo before it died in the atmosphere of Deep Space 9.
In the episode The Alternate, the Bajoran scientist Mora Pol brings Odo news of DNA traces resembling his own on the planet L-S VI. Odo, Mora, Jadzia Dax and Doctor Weld Ram travel there by runabout and find a carved stone pillar and a tiny lump of living matter beside it.
An earthquake releases volcanic gas as they beam out. Back on the station the lifeform grows, appears to change shape, breaks out of its container in the science lab and disappears into the ventilation system. It is later found dead, unable to survive in the station's environment, and analysis shows it was only a distant analogue of Odo.
The attacks that follow are not its doing: the gas from L-S VI has affected Odo, who transforms into a violent creature while regenerating, driven by his resentment of Mora.