Atlans are gigantic Sentinel battle mechs, resembling a likeness of an Argenta warrior clad in green armor with a horned helmet. Atlans can be armed with large spears and/or cannons fitted on the shoulders or in the hands, which are capable of killing lesser Titans such as Hell barges; this combined with their size suggests that the Atlans were created as a means of anti-Titan warfare. Though typically powered by Argent energy, the Atlans were still in service during the Argenta Civil War, which implies they can function on Sentinel energy alone. The method by which a pilot enters or leaves an Atlan is unknown, as Atlans have no visible cockpit hatches and there are no depictions of anyone entering or leaving an Atlan.
Multiple Atlans and pieces of Atlans appear in the Hellified portion of Exultia. The Doom Slayer uses Sentinel power cores to activate the weapons on these Atlans and clear obstacles blocking his path.
An Atlan torso is kept in the Fortress of Doom, though its connection to the Slayer (if any) is unknown.