The regular Scout robots are the most common bots in Mann vs. Machine. Like the regular Scout, they are fast but weak. To counteract their fragility, they often come in large numbers. Scout robots in early waves wield only the default bat, making them a very minor threat. However, they can easily overrun a player in numbers if they get too close. Later, these robots are seen to wield the Scattergun, making them more dangerous up close. Scout robots are intended more for running the bomb to the hatch rather than to pose a true threat to players, though it's still dangerous to get mobbed by Scout robots. In more advanced difficulties they sometimes appear with a permanent Crit boost, making them even more dangerous.

Soldier bots behave like human Soldiers, rushing into battle using with their Rocket Launchers as a primary means of attack. By itself the Soldier bot isn't a terrible threat, but nothing in this game mode comes "alone". A squad of Soldier bots becomes a quick problem as you may be faced with a barrage of rockets coming your way. Soldier Robots reload when they have time, and fire when they see an enemy.

These robots are equipped with a Flame Thrower and attack up close. They may use their compression blast to deflect rockets, including those of Sentry Guns, but they will not use it to extinguish teammates on fire. When Giant Robots appear with Pyro robots, the Pyros will cluster near the giants at the beginning of the wave and eventually scatter. Some Pyro Robots constantly shoot fire regardless of whether there are enemies nearby; this is typically done to both make a Spy's job more difficult and to light the arrows of Bowmen.

Your standard run of the mill Demomen wielding Grenade Launchers. They often appear in large numbers and can pose a great threat to anyone unlucky enough to be caught in their hail of grenades.

The basic Heavy Robot, manufactured by Gray Mann. These robots are similar to the normal Heavy: big, tough, and pack a punch. The regular Heavy wields a Minigun, ripping anyone who dares to come too close to shreds. The Heavy robot often comes in small to medium sized waves, often accompanying other robots as support. They appear to have a delayed sense of enemy tracking, meaning that they will find it hard to hit a player dodging at close range.

*Spawns by teleporting onto a sentry nest location
*Builds a teleporter exit that acts as a forward spawn point

The Engineer robot is a support unit, its arrival and destruction being announced by the Administrator, as well as by a large beam of light that appears where it spawns. It has 500 health, four times that of the standard human Engineer. Its main role is to build teleporter exits so the robots can spawn closer to the bomb. The Engineer spawns by teleporting onto a suitable sentry nest location near the bomb (if the bomb has not moved up far enough, the Engineer will not spawn), and immediately builds a teleporter exit and a Sentry Gun; players too close to the Engineer's appearance are knocked away instead of being telefragged. The Sentry Gun instantly upgrades itself to Level 3 upon completion, while the Teleporter, a Level 1 with doubled health, acts as a forward spawn point for entire groups of robots, giving them 5 seconds of invulnerability once they appear.

In some missions, the Engineer spawns normally, instead of instantly appearing at a build spot. These Engineers have less health, and are not announced by the Administrator. Unlike standard Engineers, they can spawn regardless of how far up the bomb has moved - if it is far back, they will randomly choose any build location on the map. These Engineers can also drop money when destroyed. Two different subtypes of these Engineers exist - one constructs both a Sentry Gun and a Teleporter, the same as a standard Engineer, while the second only constructs a Sentry Gun. The two subtypes are otherwise identical.

As the bomb moves forward, the Engineer will attempt to move up with it, setting up new bases closer to the objective. Just as other robots have infinite ammo, Engineer robots never run out of metal – as soon as its building is destroyed, it will construct another. As neither it nor its allies require ammo, it will never attempt to build Dispensers. Upon destruction, including the end of a wave, the building fragments will provide ammo for the players as a human Engineer's buildings would. If the Engineer is separated from its buildings, or is simply moving to a new build spot, it will completely disregard enemy players instead of trying to defend itself with its Shotgun or Wrench.

As a support robot, Engineers are not programmed to move towards the bomb by default, only becoming the carrier in rare, mainly accidental circumstances; if it does become the carrier, the Engineer will only attempt attacking with the Wrench if players are within range – and even then, it will not actually move to the bomb hatch, instead going back to maintaining its buildings.

When an Engineer's teleporter is active, an icon appears on the HUD, and it can easily be found with the blue pillar of light that appears above the Engineer's sentry nest. The Administrator will announce if an Engineer is destroyed but still has an active teleporter on the field.

*Spawns with full ÜberCharge
*+100% faster ÜberCharge rate
*+400% faster heal rate
*Übercharge lasts 8 seconds (normal)
These Medics don't appear often as other robots, but when they do, they usually accompany Giant Robots, sometimes even as many as twelve Medics on one Giant. Über Medics are equipped with a Syringe Gun, Medi Gun, and Bonesaw. They spawn with full ÜberCharge and will deploy their charges on whatever robot they are healing as soon as the Medic or patient takes significant damage, although it is both possible and often desirable to inflict enough damage in a single attack to kill the Medic without giving them a chance to deploy their Übercharge. There are two kinds of this robot: one has a very fast heal rate, and the other has a much faster charge rate, but a slower heal rate and an ÜberCharge that lasts three seconds shorter. When Medic robots are separated from their heal target or cornered by a player, they will fight with their Syringe Guns and look for their patient.

Regular Sniper robots appear in small numbers and behave like human Snipers, offering support to their teammates from afar. A notification appears when Snipers spawn, and players may yell "Sniper!" to alert their team to the robot's presence.

Sniper robots never carry the bomb, preferring to use their Sniper Rifles to hit players from afar. Their rifles emit lasers indicating where they are aiming and giving away their position. Snipers may relocate to avoid grenades and rockets but will rarely do so to get a view of their enemy, so players occupied with other robots like Tanks are advised to stay out of the Sniper's sights. If players get close to a Sniper robot, it will attack the player with its Kukri. Backing away from the robot will result in it using its Sniper Rifle to kill the player.

Their aim is deadly accurate, so they will always hit a player in sight and not taking rapid evasive action, such as strafing quickly back and forth or moving quickly left after moving right for a short time. However, they can't deal headshot damage and will usually not wait to charge their rifle, giving players a chance to ambush the robot.

Spy robots behave much like a human Spy would, sapping Engineer buildings, backstabbing players, cloaking, disguising, and using their Knife in close quarters. Unlike other robots, the Spy bots spawn where the players aren't looking in close proximity to the players, as opposed to on the map's normal spawn points. Spy bots are almost always used as support, never attempting to pick up the bomb. In a few missions, though, they appear as a normal part of the wave, and will go for the bomb if necessary, defending themselves with their Revolvers if intercepted by players.
When a Spy robot spawns, it will already be cloaked and disguised, though it will never attempt to disguise as a class the RED team does not possess. When disguised, Spies will not attack unless they're closing in on a target or the players attack first. When fleeing, Spy robots will Cloak, move a distance away, then redisguise. However, if they're very close to the player when recognized as an enemy, Spy bots will strafe within stabbing reach around the player until they get a backstab in. Exposed Spy bots almost always use their Knives - they will only use their Revolver if they are caught sapping a building or if they are going for the bomb.
Notably, Spy bots are distinguishable from regular players due to their voices. Even while disguised, they will taunt nearby players in the voice of a Spy, revealing their location to anyone paying attention. They also chuckle loudly upon redisguising, which can be heard throughout the entire map. Spy bots can also be revealed by players of the same class - human Spies cause all cloaked Spy bots in a large radius to become partially visible, as if they were taking damage.
A notification is always shown when a Spy enters the map, and its entrance is announced by the Administrator. Killing a Spy robot results a notification by the Administrator of how many Spy robots are left on the field, unless there are more than five remaining.

The Sentry Buster is a specialized robot that appears in the Mann vs. Machine mode when a Sentry Gun has dealt significant damage to the robot horde. It appears as a large pair of legs similar to a Demoman robot, but with a large naval mine for a torso.
Once a defending Sentry Gun has dealt either 15 kills or 3000 damage to the robot horde (by default), a Sentry Buster will be dispatched; they do not appear under any other circumstances. Once deployed, the Sentry Buster will make a beeline for the Sentry Gun that triggered its appearance. Upon reaching its target, it crouches and begins beeping. A few seconds later, it detonates in a massive explosion guaranteed to level the offending Sentry and just about anything else within approximately a three-Teleporter radius, including other robots around it.
While inattentive Engineers will be sure to lose at least their Sentry to a Sentry Buster, aware ones with a competent team can deal with it without too much trouble. Sentry Busters can simply be killed before they reach their target, which will cause them to wind up and explode prematurely. Hauling the target Sentry out of the detonation zone will save it, as Sentry Busters cannot move once they begin counting down, but will not protect any other buildings that may be nearby. Should the Engineer be daring, he can pick up his Sentry and carry it around the map, which will cause the Sentry Buster to chase him indefinitely until it gets close enough to explode; this does, however, stop the Engineer and their Sentry from attacking the rest of the horde. Knockback can keep a Sentry Buster at bay long enough to destroy it, but once they begin the detonation process, they are immune to it. However, regardless of how a team defeats a Sentry Buster, the robot horde will continue to send them out after a mission-specific delay time until the target Sentry is destroyed or the wave is completed. As a result, it may be preferable to allow it to do its work and simply build a new Sentry Gun.
Sentry Busters will spawn against and target Mini-Sentry Guns, but they will ignore Disposable Sentry Guns, even if it is doing more work than the primary one. If a Sentry is destroyed before the Sentry Buster gets there, it will continue running to where the Sentry used to be and detonate. One Sentry Buster can spawn for each Engineer on the defending team.
Destroyed Sentry Busters, whether by themselves or by the players, leave no money. A large cloud of dark grey smoke lasting a few seconds remains after detonation, blocking the view of players within the range of the smoke.

Tank Robots (referred just as Tank) are large bomb-carrying machines that arrive with the robots in Mann vs. Machine modes. They carry no offensive weapons and thus have no direct way of harming the player. They can take an extreme amount of damage before they are destroyed, far more so than any other robot. The Administrator announces the entrance, progress, and destruction of each tank.
After entering the map, tanks slowly travel along a set path to the bomb hatch before deploying their bomb and ending the round. This path is unique to each map and may differ from the path of other robots in the wave, if any. They have their own bomb, independent of the one carried by the other robots, and in waves with tank(s) and bomb-carrying robots, both the tank and the robots must be destroyed to complete the wave.
Tanks are immune to all effects outside of damage and critical hits; they can only be stopped via destruction. They cannot have their movement interrupted or slowed; standing in front of one will simply push the player away for no damage, while players that cannot be pushed away due to walls or props are crushed to death, and buildings in the way are destroyed. They cannot be burned or soaked by Jarate or Mad Milk, they do not give metal to Widowmakers, they cannot be sapped or marked for death, they do not give health to players buffed by the Concheror, and they have no heads to shoot or backs to stab. Finally, they resist 75% of Minigun damage, severely reducing a Heavy's damage output against it.
Tanks have a health meter below the "robots remaining" display on the HUD, and as they are damaged, they will acquire bullet holes and cracks and lose parts, like the covering on their treads. The final tank of a mission has distinctive white stripes; this does not correlate to any of its properties.