In Mass Effect 2, Illium serves as a key location where players can initiate several significant missions. Among the primary missions are Dossier: The Assassin, which involves tracking down a notorious assassin, and Dossier: The Justicar, focusing on a powerful warrior bound by a strict code of ethics. Another critical mission is Miranda – The Prodigal, which delves into the backstory of the character Miranda Lawson, unveiling her ties to the Illusive Man and the Cerberus organization.

In addition to these main missions, Illium offers side quests that enrich the gameplay experience. Two notable side quests are Illium: Liara: System Hacking and Illium: Liara: The Observer, both of which revolve around the character Liara T’Soni and her pursuits on Illium. These quests provide players with opportunities to engage in the world-building of Mass Effect 2 while exploring personal stories and the intricate relationships between characters. Overall, Illium plays a crucial role in both the narrative and gameplay of the game.