There are several Battlefield Units, also known as non-playable characters, on the field at any given time, with different abilities, AI programming, and alignments. The inclusion of these NPCs function both to make the combat more complex and interesting and to make strategies take both the human and non-human perspective into account.
Marvins are the ubiquitous non-playable enemies in Titanfall, and are manufactured by Hammond Robotics as workers. According to the Hammond Robotics site, Marvins are actually called MRVN Automated Assistants.
Spectres, unlike their counterpart Marvins, are autonomous "grunt" units for the Militia, and are designed specifically for warfare. Whereas the Marvins are workers first and fighters second, the Spectre class of autonomous units are designed specifically for fighting, making them formidable on the battlefield. Unlike the Marvins however, Spectres are controlled via built-in programming and artificial intelligence as opposed to remote control by a general or commander; while this makes them highly independent and useful for incursions into the line of fire, this removes the ability to control them en masse, which can be a disadvantage in certain situations. While they are generally easy to take out, their resilient body makes it so that it does take a little bit of punishment. The good news about Spectres is players can hack them with their data knife to create a personal army.
Designed for massive battlefield carnage, the Heavy Turret is a securely mounted weapon found most often braced in urban environments atop buildings and bridging chokepoints. With a considerable range of motion and advanced AI allowing for excellent target acquisition and tracking, Turrets are an important asset for a team in combat. Be wary though - the turrets are hackable, and can be turned against the team that owns it through the use of the Data Hack ability of the Data Knife.
Ziplines are lines strewn across certain maps which allow for the quick travel from edge to edge in combat. The lines can be used in both directions, and is most useful during the Capture the Flag mode as entry and exit points for the flag locations.