Longtoothed Slideclaws - Golden Treasure: The Great Green

The Longtoothed Slideclaws were at one point a group of proud hunters, slaughtering their way through the frozen lands feasting on the great beasts that roamed there. But, then the no-tails arrived, and they hunted the great beasts even moreso than the Slideclaws, until there were no great beasts left, and the Slideclaws starved. They tried to move, but then the no-tails moved to slaughtering the Slideclaws, until the very last Longtoothed Slideclaw was killed. Using their fury as hunters, the Longtooths latched their spirits onto the no-tail that did the final blow, and moved south to gut as many pure spirits as they could find so they could maybe revive their Way.

Soldiers of the giant war - Unexpectables

Technically not *their* killer, but Might-Crank was an automaton soldier used against the Fire Giants in the giant war, and killed many giants before it was finally killed. Fighting alongside Might-Crank were regular soldiers, many of whom also died in the battle where it was destroyed. The sheer amount of bodies strewn across the battlefield, both giant and non-giant alike, basically had Might-Crank be buried under the corpses of the fallen. Eventually, the soldiers possessed the automaton, and when people tried to retrieve it to bring it back for a new war, they lashed out thinking they were still fighting the giants.

Spirits possessing the body of their killer