During your adventure in the Borderlands 3 Revenge of the Cartels event, you have to go after a crime boss who is out to get Maurice. Because he’s asked for your help, you’re more than happy to lend him the assistance. When you make it to the Cartel’s hideout, you have to explore the large mansion to complete a variety of different challenges. One of these challenges is Locked In Here With Me, and you need to take out six of the underbosses in the game during a single playthrough.
You can find them throughout your playthrough of the main quest of Revenge of the Cartels. For example, the first underboss you encounter greets you when you make your way towards the front entrance of the large mansion. After you take it out, you gain access to the large building. But now, you have to find a fountain headpiece to proceed further into the mansion to find the crime boss. You can find the piece on the second floor of the villa by going up the stairs at the front entrance and taking out the underboss guarding it. Once you have the fountain piece and reattach it to the fountain, you have run into at least two of them.
However, once you go down the fountain, you face the boss. That’s the end of the run, and you start over. You don’t want to do that to complete this challenge. Instead, start exploring the mansion. There are several locations you can visit to find other underbosses.
The notable location you can find these underbosses include the Garden Plaza at the back, and the Mansion in the Mansion, on the right side of the map. These locations contain at least one additional underboss. After you investigate these areas, proceed back to the fountain at the entrance and go after the crime boss.
While fighting him during the encounter, he summons minions and additional underbosses to assist him in taking you down. When you take down these underbosses during the battle, the challenge should successfully tick off for you in your notifications, and you don’t have to worry about it anymore.