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Heavy Soldiers, often referred to as "shields", are close quarter combatants armed with a riot shield, pistol and baton. Their primary tactic is to close the distance between themselves and a player in short charges using their shield for cover and the pistol for offense. When within melee range, the pistol is unequipped and the riot shield is used to knock down the player who they then proceed to strike repeatedly with their baton. On regular and easy difficulty it is possible for the player to draw his or her pistol after being knocked down thus limiting the effectiveness of the attack. In hardcore and skilled missions a team mate is required to end the attack or else it will continue until the player is dead. After the attack is finished there is a brief period where the player will not be able to stand back up unassisted.
A player cannot be knocked down while on stairs or if their back is against either a wall or any object greater than waist height. It is easiest for the medics to exploit this weakness as they can heal themselves faster than a Heavy Soldier can damage them with repeated shield bashes and because the defibrillator will kill them instantly.
CQB's are close quarter combatants armed with a pump action shotgun. They are perhaps the most aggressive of all the standard enemy soldiers and once they engage a target they will often only seek cover in response to grenades. Their primary attack is a single unbroken charge towards the player ending with a series of shotgun fire when in close proximity. On easy and regular difficulty they are considered by many to be the least challenging enemy to deal with due to their slow aiming speed and severely limited range. This changes dramatically when the difficulty is increased to hardcore or skilled where their range and damage is increased significantly. In hardcore missions it is not uncommon for a single CQB to catch players by surprise and wipe out most or even all of a team (although this is due in part to the CQB getting so close to a cluster of players that many briefly hesitate to shoot, fearful of killing a team mate with friendly fire). They are particularly weak against engineers.
Assaults are mid range combatants armed with, as one might guess, an assault rifle. Risk adverse, they tend to stay near cover when possible and will usually only close the distance between themselves and a player if the team falls back or remains out of optimal range for a period of time. If a player gets within 2 to 3 meters of an Assault they will stop shooting and charge in an attempt to kill the player with the butt of their rifle. They are particularly weak to riflemen and engineers.
Demomen, often called rpg's, are mid to long range combatants armed with a rocket launcher. Highly risk adverse, where possible they will only break cover for a single shot. They tend to hide on balconies and rooftops and are generally only found on ground level when playing vehicle escort type missions. Demomen can be tricked into suicide if a player can place his or herself just to the periphery of the object they are hiding behind. As an example, if the demoman is launching from a balcony, a player can sprint forward until they are against the wall of the building and then slowly walk backwards until the demoman takes a shot. If done correctly he'll clip the edge of the balcony and blow himself up. They are particularly weak against snipers and, as explained, themselves.
Snipers are long range combatants armed with a low caliber pistol and a single shot sniper rifle. Not risk adverse, snipers will rely on distance for protection and will rarely take cover even when fired upon. Like demomen they are typically found on roof tops and balconies. They are particularly weak against snipers and riflemen.
Specops are long range combatants armed with a high power semi-automatic sniper rifle. Due to the difficulty in killing them and the tremendous amount of damage they can do, Specops are arguably the most feared of all the standard enemy soldiers but also, fortunately, the rarest. Not even remotely risk adverse, Specops will rely on blinding players with a high intensity laser sight for protection and will not take cover, sometimes even when a grenade is thrown near them. While somewhat dangerous on all difficulty levels, in Hardcore missions, much like CQB's, they are more than capable of single handedly wiping out an entire team of players. They are weak against a combination of smoke grenades and riflemen wielding high capacity machine guns such as the z84mg.
Heavy Gunners appear on nearly all skilled and hardcore missions. They are a mini-boss that require some skill to take down. The heavy gunners one weakness is their illuminated backpack. This is their power source and the key to defeating them. When firing at the backpack, it is better to aim and shoot the backpack when using a shotgun as it ensures the most damage possible is dealt. Two strategies can be employed depending on the difficulty of the mission. For regular missions, it is often simple enough to have a medic 'tank' (lay in front of the gunner)and have the rest of the team to shoot at the heavy gunners backpack. The other strategy that works in most situations is to have a player spin the gunner and this leaves the exposed backpack to shoot for the rest of the players. After spinning for a while the gunner has to reload and this is the perfect opportunity to take aim at the backpack and bring the gunner down. Medics can also employ their defibrillator to deal significant damage on the gunner(the defibrillator does not have to be in contact with the backpack for the gunner to be damaged) .
The MECH 2300 is a boss that appears in all 3 locations, it is a land boss that fires missiles at your team. Find cover to avoid the barrage of missiles and take it down. It is one of the toughest bosses in the game and requires a good team to take down. The method to take down the MECH is as follows, first one has to fire RPG's (weapons only work in regular)at the MECH's cockpit (blue area, near its chest) which is essentially its shield. After three hits, the MECH will fall to it's knees and its shield is not powered for a few seconds. One can then see a blue illuminated area at the top of its head which is its weakness. Some fire power here will lower the MECH's health, the damage taken will depend on the difficulty. This process is repeated over until the MECH loses its health and is destroyed. In regular missions, a machine gun can help reduce some of the MECH's resistance. The primary strategy that is used to take down this boss is by spinning him allowing the rest of the team to wait and shoot the rpgs. When shooting the rpgs, make sure to shoot just as the MECH's cockpit turns to ensure the barrier is weakened. Some maps have certain areas where the MECH's rockets get bugged and this can also be a strategy to take down the boss. At the end for a few extra points, you can slide kill the MECH.
The KA-50 Gunship or otherwise known as 'Heli' is another boss that you can face on a PVE mission. It is an agile, fast flying helicopter that circles above you with machine gun turrets and missile launchers. To beat this boss, it takes a good team and making use of the coverage that the map gives. To kill this boss, you need rpgs, these spawn at specific points on the map. At the same time there maybe other bots that can provide a hindrance and thus good covering fire is needed. To kill the boss, one needs to fire a certain amount of rpg's at the boss depending on the difficulty to reduce its health. Firing the rpgs is all about timing and making sure that if the heli is moving to lead on the shot. There is usually a check point once the Gunship has lost over half its health. On hardcore missions, it is challenging as the boss is more resistant to rpgs and thus it will take more shots to destroy it but as long as the team remains in good cover, it is relatively simple to take down. Be careful when the gunship flys over you as the turrets can kill you very fast.