Much larger than Hulks, Juggernaughts were the largest units that face the player in combat during the Marathon series.

David "Candyman" Candland of Bungie in a netgame of Marathon. The weapon being fired at the player is the missile launcher. The weapon the player is using is the flechette gun. Introduced in Marathon 2:Durandal, the flechette was a fast-firing weapon that would work underwater, making it many times preferable to the MA75B assault rifle; however, ammunition for it was often scarce.

Marathon Infinity extended the armed BOBs from Marathon 2 by giving them spacesuits, allowing them to fight in airless environment, hence the term "vacuum BOB" or "VacBOB" for short.

Marathon Infinity was particularly well known for its highly detailed and distinctive textures. Here is a multiplayer level featuring the so-called "Jjaro texture set" used in the game. The Jjaro, a mysterious, nearly omnipotent race that has disappeared from the universe in the Marathon series is widely speculated to be analogous to the Forerunners in the Halo universe.

Games in the Marathon series featured environments that were sometimes underwater, or, as in this shot, in vacuum. Only certain weapons, such as the fusion pistol shown above, would work in a vacuum; projectile weapons that depended on gunpowder like pistols and shotguns were useless. All the BOBs equipped for vacuum combat, like those above, toted fusion pistols.

Both Halo and Marathon have groups of aliens which are color-coded as a kind of indication of rank. The tall, armored Hunters of Marathon were no exception, although in the first Halo game it seemed as if there was only one group of Hunters (blue).

Automate drones like 343 Guilty Spark and the Sentinels were another item that appeared originally in the Marathon series. The first "security drones" in Marathon 1 were large, clunky, mechanistic devices. Marathon 2 featured much cleaner, organic-looking designs. Eventually the look changed even further, as seen above, with these dramatic, almost manta-ray like drones.

As in Halo, Marathon had several ball-objective games where the ball was represented graphically by a skull.