The dungeoneering party simulator is an Invention device that is a part of the cave goblin tech tree. It requires 55 Goblin Currency and level 70 Invention to unlock. It is a consumable device that increases the Dungeoneering experience gained for completing Dungeoneering floors in parties of four or fewer players.
Upon completion of a Dungeoneering floor with a party of 4 or fewer people, the device is consumed from the first player in the party who has one and the party size modifier for the floor is increased by 1. For example, upon completing a floor alone (Difficulty Modifier 1:1) the modifier would be increased to the difficulty for two people (Difficulty Modifier 2:2). This affects all players in the party, not just the one using the item. It doesn't need to be equipped for it to be used.