Underworld Overseer is a strategy simulation game that puts players in the shoes of a powerful Overseer tasked with managing an underground lair. The goal is to build and maintain this underground fortress while defending it from waves of invaders, such as adventurers, who seek to infiltrate and destroy it. Players are given a number of tools to help them in this endeavor, including the ability to create different rooms for minions, set traps, and cast spells. These mechanics combine elements of real-time strategy and classic tower defense, all in a setting where the ultimate goal is to outwit and defeat those who dare to delve into the depths.