The Maulers of Undermoutain is a group of adventurers that will come into the Helm and Cloak tavern in Baldur's Gate Northwest immediately after you talk to Gorpel Hind and his Band of Merry Fools at the bar. The party consists of Nader, Caturak, Wilf, Arlin, Pargus and their leader, Gretek. When they enter, Gretek will initiate conversation with your party member that is closest to the door and no matter what you reply Maulers will become hostile. If you have chosen conversation option 1 in the talk with Gorpel Hind, then the Merry Fools will help you in the fight and leave after it. Choosing option 2 results in them leaving immediately so they wont help you.
One of the good tactics for this fight is having your fighter near the door and the other party members further away before starting conversation with Gorpel, as after the Maulers arrive, they will all be in one place. Give your fighter as much fire resistance buffs as you can through potions, items and/or spells and, after the Maulers come, cast fireballs in the area. If you have a good-aligned party, watch for civilians, as killing them results in a large Reputation loss. Killing the whole party results in total of 5250 XP, 214 gold pieces and many items including the Battleaxe of Mauletar, Bracers of Defense A.C. 7, Adventurer's Robe and a Long Sword +1.