Scooter wants someone named Shorty dead and says he can be found hiding at a place called Stalker Hollow, which is located in The Fridge area. When you get to the marker, you find out that Shorty was lunch for a Stalker named Sinkhole, who takes off running as soon as you approach. It’s possible for the mission to glitch if you try to kill Sinkhole as soon as you first see it.

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It’s easy to tell where Sinkhole is located because of Shorty glowing in its belly (left). Kill Sinkhole to free Shorty, then proceed to kill Shorty (right).

So, it’s best to let him escape and to just fight through the normal Stalkers until you get to the end of the area. Although Sinkhole is invisible, it’s easy to spot him because of the glowing Shorty in his belly. There is an optional objective to kill Sinkhole with a shock-type weapon, so if you have one on you, use it. After Shorty is set free, he repays you by swinging his little Psycho arms at you, so feel free to swing back. Return to Scooter once Shorty is dead.