Undead rancor

The undead rancor was a large rancor mutated by the Blackwing virus living during the Galactic Civil War. The creature was the result of an ill-fated experiment conducted by the Imperial scientists of the Imperial Research and Prison Facility on Dathomir after the Battle of Yavin. In 1 ABY, an accident took place in the Imperial Research Facility and the Blackwing virus escaped containment. The virus killed most of the people in the area, turning them into undead creatures. At that time, the undead rancor lived in the caves below the Imperial Research and Prison Facility. The creature was eventually defeated by a band of spacers who explored the Research Facility during the epidemic on Dathomir. In the Rancor's caves, the spacer discovered several Blackwing crystals, which could be used to produce a smoke-colored lightsaber blade.

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