Blue is an enzyme and the main character of the Test Subject series. Blue is also called Test Subject Blue, or Test No. 0001232423545 by the professor. Blue also appears as a boss in the game Nitrome Must Die.


Blue is a blue enzyme with two black eyes. Unlike the other enzymes in the Test Subject series, Blue takes the shape of a teardrop.

Game information

Test Subject series


Test Subject Blue

Blue started off as an experiment by the professor in Test Subject Blue. He put Blue through twenty-five tests, trying to see what the enzyme was capable of.

After completing all twenty-five tests, the professor decided to merge a blue and orange enzyme together, thus creating the green enzyme.
Test Subject Green

From the newly created green enzyme, the professor tested it out against Blue. When carrying out the third test, the sirens within the lab went off and the professor abruptly disappeared. Blue managed to complete this test and the professor tried to carry out the next but lost hold of Blue as he injected him into the start cylinder.

Once Blue approached the food pill, it was snatched by Doctor Nastidious and taken to Doctor Nastidious' base.

Eventually, Blue would be taken to Nastidious's secured test lab and injected into another suit, Rex209, as seen in the ending.
Test Subject Complete
Penguin 1

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Blue is placed inside Rex209, a mechanical suit which is more advanced than the proto-suit, by Doctor Nastidious. In Rex209, Blue is now able to walk on the bottom of platforms and shoot more powerful proton bullets. Doctor Nastidious continued to test Blue with his test chamber. However, one day, the doctor leaves for the professor's laboratory, leaving mercenaries to run the experiments on Blue.

The mercenaries are much more careless. They laugh and make faces at Blue outside of the test chamber. Eventually, they begin to interfere with the tests themselves, placing worm orange enzymes inside the test chamber. Then, when one mercenary goes as far as to place his hand in the test chamber and crush Blue if it tries to escape, Blue shoots the mercenary. This cause the mercenary to become surprised and knock the test chamber over, allowing Blue to escape.

Blue then traverses throughout Doctor Nastidious' laboratory, traveling from room to room via transporters and avoiding enemies and hazards along the way. Eventually, Blue manages to find the professor, with the help of Rex209. However, the professor is dead. Blue is saddened by this discovery and remembers the experiences it had with the professor.

Test Subject Complete The Dead Scientist

Test Subject Complete The Dead Scientist

The dead professor scene

However, before Blue can escape, sirens sound and Doctor Nastidious traps Blue inside a glass jar. Blue manages to escape this jar and jump into a transporter by sneaking out while the mercenaries were not looking. However, as Blue jumps out of the transporter in the next room, it finds that The Machine, Doctor Nastidious' assistant, has awoken. The Machine wants to destroy Blue and tries to for several tests by shooting its laser at Blue. However, Blue escapes every time.

Meanwhile, Rex209 tells Blue that it has made a remarkable discovery - hidden deep in its hard drive is an encrypted file labeled "Serum BLUE1207". The file states that Blue was not made to fight. Rather, Blue is the essence of life itself - Blue was made to heal. With this discovery in mind, Blue and Rex209 head back to the dead professor's body. Rex209 shuts down, telling Blue to save the professor. Blue is saddened by Rex209 shutting down, but it knows what it has to do. Blue stands up straight, saluting the deactivated Rex209. Blue then jumps toward the professor's mouth, sighs, then jumps in, reviving the professor. Blue was then most likely digested by the professor's body.

Test Subject Complete - The Revived Scientist

Test Subject Complete - The Revived Scientist

The revived professor scene

In game

Test Subject Blue, Green, and Complete

Blue appears as the main character in the series. It is the only playable character. The player controls Blue with the arrow keys to move and the spacebar to shoot a proton bullet. Pressing the left or right arrow key will move Blue left or right, respectively. Pressing the down arrow key will cause Blue to crouch, and pressing the up arrow key will cause Blue to jump. Normally, Blue can only walk on the top of platforms. However, in Test Subject Complete, Blue can walk on the bottom of platforms as well. If Blue comes in contact with a hazard or an enemy, then it will die and respawn in the most recently activated spawn cylinder.

In order to complete a level in Test Subject Blue, Test Subject Green, and levels one to six of Test Subject Complete, the player must move Blue first towards the key card of the level. The key card will then open up the food pill container upon being obtained. Then, the player must move Blue to the food pill, which will allow the player to progress to the next level upon being obtained.

However, in levels seven to twenty-five of Test Subject Complete, the level objective is different. In level seven, the player must make Blue shoot the mercenary's hand in order to escape the test chamber. In levels eight to twenty-five, the player must move Blue to the transporter of the level in order to complete the level.

Penguin 1

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In levels twenty-six to thirty of Test Subject Complete, Blue does not appear. Instead, the professor is the main character of those levels.

Test Subject Arena

Blue also makes an appearance in the spin-off Test Subject Arena, facing off against Green from the sequel. The spin-off introduces a new melee attack where when it can attack Green within a very close range. Instead of shooting with the proton gun, Blue will slash Green with an extended piece of its gun. Blue acts exactly as he does in the Test Subject games.

Test Subject Arena 2

Blue appears in Test Subject Arena 2, retaining his exact behaviour from Test Subject Arena.

Upon completing his single player course, the following quote is provided: "Well done Blue, Professor would be so proud of you." Unusually, this quote (from how it is written) is not spoken by Blue, but rather by someone who is watching the test. This person may be the Mercenary watching the test.

Nitrome Must Die

Scientist and BlueBlueRex210NMD
Blue in Nitrome Must Die, in its proto-suit (top) and in Rex209 (bottom)
Attacks Firing proton bullets
Level Forty
Game(s) Nitrome Must Die

Blue appears in Nitrome Must Die as the fourth boss of the game. Blue is held by the professor, whose hand is reaching out of the wall. He will move the enzyme in its suit vertically up and down the wall.

Phase one

Blue attacks by simply firing its proton gun while the professor moves it up and down. After having its health lowered down to three-fourths, Blue will create a proto-blade out of his gun and fire several large homing proton bullets at the player, which can be destroyed by the player's weapons. Destroying these bullets can be used to protect Austin and Justin, but can render hitting the boss more difficult.

Phase two

After lowering Blue's health down to one-third, Blue will perform another homing bullet attack, this time with quicker and more abundant bullets. Then, it will switch into the Rex209 and fire more rapidly. Blue will continue to fire blue proton bullets continuously while on the screen, without moving vertically and only stopping when the professor pulls it back off the screen.

After Blue's health is fully depleted, the hand will move vertically up and down, then explode. After a few seconds, it will fall and be slowly pulled off the screen.




In the first two games of the Test Subject series, Test Subject Blue and Test Subject Green, Blue performs its tests in a mechanical suit known as the proto-suit. The proto-suit was designed by the professor and allows Blue to shoot proton bullets for defense and move freely around its surroundings. Blue is also given the ability to jump and crouch to avoid enemies or hazards. However, the proto-suit is fragile and will shatter easily, killing Blue in the process.

In Test Subject Arena, the suit gains a special melee attack which also is present in Test Subject Arena 2. When attacking close to an opponent, a solid proton beam will form and extend from the suit's gun, slashing the foe. Blue will extend this beam upwards when performing his victory pose in both games as well. Moreover, Blue also uses this proton blade in Nitrome Must Die to concentrate proton energy and shoot larger homing proton bullets at Austin and Justin. Although the proto-suit seems capable of producing this beam easily, the proton bullets will still remain as Blue's primary form of attack when in the suit.


In the game Test Subject Complete, Blue is removed from the proto-suit and is placed inside a new mechanical suit, Rex209, which was designed by Doctor Nastidious. Rex209 has all of the capabilities of the proto-suit (except for the melee attack), with some extra features and changes. First, the proton bullets that Rex209 fires are much quicker and will fire at a faster pace, allowing Blue to kill enemies quicker. Second, Rex209 has the ability to walk on the bottom of platforms and on ceilings. These improvements over the proto-suit are, however, counterbalanced by a decrease in speed and mobility. If the Rex209 suit is destroyed, it will break apart into several pieces of metal and glass. The suit will then reassemble at the last spawn area that was activated or at the beginning of the level if no spawn areas were activated.


In the Test Subject series, Blue's occupation is being the test subject of two people - the professor and Doctor Nastidious. In each test, Blue is spawned and placed in its suit by a spawn cylinder. In each level, Blue must navigate itself to a food pill, which at the start of each level is surrounded by a glass capsule.

To deactivate the glass capsule, a key card will be obtained. Blue can now obtain the food pill, which Blue will pick up when it gets near the food pill. Blue will then be sucked up by a syringe to be transported to the next level. Blue may have to use other objects to get to the key card and food pill. Also, while accomplishing these tasks, Blue must avoid all enemies and hazards, or else Blue will die and respawn.

Other appearances



  • When Blue stands in one place for a set amount of time, it will throw itself up against the glass in its suit twice, creating cracks, which will quickly disappear after Blue shakes its head.
  • Blue seems to be a rather advanced enzyme, as it is shown that he is capable of thought, memories, and emotions.
  • In Test Subject Arena, Blue gains a special melee attack where it will slash Green with a piece of proton extending from its gun. This melee attack has not been used in any other game in the Test Subject series.
  • Although enzymes don't have an exact gender, Blue is referred to be male in the Test Subject series.
  • Blue bears a strong resemblance to the main character in the video game Dragon Quest Heroes: Rocket Slime.
  • Many Nitrome games have slime enemies that look similar to Blue, including Knight Trap, Office Trap, Nitrome Must Die, and Blast RPG.
  • Spoiler
    Although the Rex209 suit first appears in Test Subject Green, its real purpose is first seen in Nitrome Must Die.
  • Spoiler
    In the ending of Test Subject Blue, the green enzyme looks quite similar in shape to Blue, although seems a bit smaller and duller.


  1. Professor/Quotes - Test Subject Blue:
    Day 7: The test scores are relative to not only the number of times Blue is killed but also to the number of enemies he kills and the time it takes to complete a test.
    Day 8: He really is quite special!
    Professor/Quotes - Test Subject Green:
    Day 1: However Blue is only as strong as the proto-suit he is in.
    Doctor Nastidious/Quotes:
    Day 18: Only until Blue completes all of my tests will he show his worth!
    Day 23: It will be a shame if Blue fails but he must be able to deal with guns for my future schemes.
    Day 29: Only then will I know for sure that he is ready!