There are many enemies that the Marine and his companions encounter throughout both games. Most enemies belong to powerful factions and fight alongside their comrades. Enemies can be separated into four different categories. The many different forces opposing the Marine have their own factions and species, and also varies in health and difficulty. All of these enemies want to kill the Marine for their own reasons and will fight to the death to see that he is stopped.
Humans are the first type of enemy seen in the Plazma Burst series. Humans are the most prominent force in Plazma Burst: Forward to the Past and Plazma Burst 2 and consists of all the Civil Security forces, along with the Human Soldiers which are specific to PB:FttP. They employ a variety of equipment to aid them in battle. The humans are native to the planet Earth, and are usually the ones defending it from alien invaders such as the Usurpation Forces. In Plazma Burst: Forward to the Past, the human soldiers reside on a planet that is not Earth. It is possible that they invaded the planet or colonized it.
These enemies are only seen in the Plazma Burst: Forward to the Past and are always seen wearing a blue armored uniform. Generally, you can tell how difficult one of these soldiers are by the helmet they wear and the weapon they carry. The helmetless soldiers are the weakest, using a Pistol C-01p. The ones with a helmet and yellow visor are in the middle being in the middle strongest using the Assault Rifle C-01r. The ones with green visor using a Pistol C-01p are in the middle as well. The strongest and most dangerous have a red visor and use the Shotgun C-01s. They carried all the same weapons the Marine could with the exception of grenades. These were low difficulty enemies, and eventually they were outclassed and replaced by Grubs and Falkoks as the game progressed.
These enemies were exclusive to Plazma Burst 2 and were different from the Human Soldiers. They are very a formidable enemy with large armies and a large arsenal of weapons. There are different types or classes of Civil Security, they include:
- Civil Security Lite - These lightly armored soldiers made up the bulk of the Civil Security Forces and are armed with light weapons such as the Pistol CS-Pro, Assault Rifle CS-RC and sometimes Lite Railgun v01 CS-HShot.
- Civil Security Heavy - These are the more armored cousins of the Civil Security Lite, although they are much slower because of the armor they wear, but they also pack a heavier punch. They tend to use weapons like the Heavy Railgun v04 CS-OneSOneK, Plasmagun CS-Bloom, Rocket Launcher CS-LitBro and CS-BNG.
- Civil Security Ghost - These special units are some of the most deadly troops of all, not because the weapons they carry but because their armor has the ability to cloak its user. They usually carry a Shotgun CS-DAZ and use their PSI Blades.
- Civil Security Boss - These are the commanders of the Civil Security armies and are the most dangerous of the Civil Security forces. Their armor provides extra protection but is made up of light material as to not impede their movement during combat, and are usually armed with heavy weaponry such as the Plasmagun, Rocket Launcher CS-LitBro, CS-BNG and Heavy Railgun v04 CS-OneSOneK, Ray Gun C-01y and Drone Gun CS-Virus.
- Falkok - These Aliens are present in the Plazma Burst: Forward to the Past campaign and are found on Level 40 of the Plazma Burst 2 campaign. They wore advanced armor that provided them with protection although it did not cover their legs. They normally carried an Assault Rifle C-01r or Rocket Launcher which they used with deadly accuracy. They also used jetpacks in the first game.
- Phoenix Falkok - These are the best of the Falkonian army. Only three exist in the Campaign. The three known Phoenix Falkoks were killed on Level 16 of the first game. They are equipped with a jetpack and a fully upgraded Plasma Cannon. They portray a striking resemblance to Usurpation Destroyers.
- Minor Usurpation Soldier - These enemies are the grunts of the Usurpation force that invaded Earth. They wear armor that offers very little protection and weapons that are not very powerful such as the Alien Pistol and Alien Rifle. Despite this, they can be deadly in large groups, and it is very unlikely to find them alone. After the first few levels of the campaign, Major Usurpation Soldiers replace these weaker counterparts.
- Major Usurpation Soldier - The backbone of the Usurpation Forces, these soldiers wear armor that provides better protection and carry more powerful weapons than the Minor Usurpation Soldiers, although they are only one step up on the Usurpation hierarchy. They carry weapons such as the Alien Rifle, but can also use any Civil Security weapons, from Lite Railguns to Plasmaguns.
- Advanced Usurpation Soldier - They wear advanced armor that provides much protection and plenty of mobility. Some use the most advanced weapons that the Usurpation Forces had to offer such as the Alien Shotgun and occasionally the Heavy Railgun, BNG or Rocket Launcher.
- Usurpation Destroyer - They carry some of the most advanced weaponry and wear advanced armor that provides extra protection and no limit of mobility. Weapons such as a fully upgraded Alien Rifle, CS-BNG and the Ray Gun C-01y can be found in their arsenal. They are mostly encountered in groups. They are not seen fighting alongside other Usurpation forces other than level 33, in which one is seen leading an attack.
Another deadly foe that makes use of its advanced technology to cause destruction. Mainly made up of Androids. It is unknown who the Androids pay allegiance to or who manufactured them in the first place; however, they are hostile to the Civil Security, so Usurpation Forces could have possibly manufactured the Androids in Plazma Burst 2.
- Grub - These yellow androids are only encountered in Plazma Burst: Forward to the Past, and are not very dangerous on Easy or Normal difficulties. Although their armor plating is bullet resistant, it still does not protect them very well. They have 2 shotgun-like arm cannons as a weapon. Grubs also make an appearance on Plazma Burst 2 as a multiplayer skin.
- Elite Grub - The Elite Grubs are the more powerful combat androids of Plazma Burst: Forward to the Past. These enemies can be dangerous, as they have fairly powerful weapons and strong armor. They wear gray heavier armor than their counterpart and use a Ray Rifle TCoRR or Rocket Launchers as arm cannons.
- Android T-01187 - These are the basic humanoid androids, a rather weak opponent. They do not carry very powerful weapons. They usually carry Alien Shotguns, however some are seen carrying Rocket Launchers.
- Android SLC-56 - These make up most of the androids. They have advanced armor but it is very light, as an explosion can send one of these units flying. They can also be easily reprogrammed to aid one in battle, which occurs during the campaign of Plazma Burst 2 at Level 37. They normally carry Lite or Heavy Railguns, or Rocket Launchers, while the ones that can be found at level 37 carry Alien Shotguns.
- Sword Bot - A large, humanoid robot with sword arms. It makes its appearance in the final level of Plazma Burst: Forward to the Past.