Borderlands 2 Walkthrough Part 53 – Highland Sidequests: Slap-Happy

Head into Moxxxi's and go over to Sir Hammerlock. He will tell you about Old Slappy. This Thresher was responsible for him losing a few limbs. While Science would demand that he forgive the creature, he ask you to be his instrument of vengeance to kill the beast that has torn the limbs from his own body. When you accept the side quest he will offer you his right arm, literally, for bait to attract the thresher. With the arm in hand head out from Sanctuary.

Head over to the Highlands – Outwash via fast travel. Head to the Marker in the Southwestern portion of the Outwash. Head to the one tower in the river that has a chain on it and hang Sir Hammerlock's arm from it. After that back up. It is time to fight a Badass Thresher in the water. Sir Hammerlock will mock and taunt the Thresher through your ECHO. The good news is none of the robots from the Plant will care about this. The bad news is you are facing down a badass thresher alone.

Focus as much as possible on shooting the eyes like Sir Hammerlock suggest. If you get taken down, focus instead on the tentacles. These have a somewhat separate health bar and are a lot easier to take down and get a Second Wind off of. Just keep firing into Old Slappy's face to get criticals by hitting its eyes. Keep moving and shooting throughout the fight. It make take a round or two, but you will take down the Thresher. Be sure to grab Sir Hammerlock's arm so you can complete the mission.

With Old Slappy dead and Sir Hammerlock's arm in town, return to Sanctuary. Head to Moxxxi's and speak with him to get your rewards.

Reward: 3859 XP, Blue Shotgun