The Proto-Suit is made of a glass pod in the middle, which Blue sits in. On the right side of the suit (when the suit is facing the right side of the screen) is a proton cannon which Blue uses for defense. On the left side of the suit is a piece of metal in the shape of an arm. On the bottom of the pod, a metal plate which holds the pod is seen, with two metal legs.
In each level of Test Subject Blue, the scientist will push a syringe into a spawn cylinder. The spawn cylinder will then spawn Blue into a Proto-Suit, which will be dropped down and release the arms hidden behind the glass jar part Blue is provided with the suit in every level of Test Subject Blue, since he cannot in any way complete the test without it, since he lacks abilities which the suit has. Blue will bounce up when moving in the suit, and will frequently crack the top of the Suit if left in one place to long.
Mimic green enzymes will mimic Blue's Proto-Suit. When Blue's suit is mimicked, the mimic green enzyme will be able to mimic all of Blue's actions, including walking, jumping, shooting, and ducking. The projectiles shot do not look like Blue's proton bullets however, but more like green enzymes with eyes shaped like bullets. Green in Test Subject Arena, the Test Subject series' spinoff, takes the form of a mimic green enzyme mimicking Blue, and also gains all the actions of the mimicked suit. He does not, however, mimic Blue's special melee attack. Instead, he causes spikes to stick out all over his body.
The Proto-Suit is armed with a proton cannon that fires blue bullets. The proton cannon is circular, with a beam sticking out that is not circular. The blue bullet substance can be seen in the beam sticking out. Blue's bullets can harm enemies and activate switches, and bounce of mirrors, as well as go through green teleporters.
Oddly, Blue's bullets can also kill him if they hit hit him again after he fires them. This danger is seen more in later levels, usually when Blue is trying to kill Dodge Orange Enzymes.
First seen in Test Subject Arena, when Blue is very close to Green and attacks, Blue will slash Green with his proton cannon itself instead of firing at Green. As Test Subject Arena is a spin-off and not part of the main Test Subject series, it is likely not part of the series in-game history.
The only functions used in gameplay for Test Subject Blue is the proton cannon and jump. Many other functions exist on the suit, some seen only in a diagram on the menu for Test Subject Blue. Almost all the functions are on the proton cannon on the left of Blue.
The bottom rectangle of the arm is a power pack, which presumably supplies the power for Blue's suit. The arm part the bottom rectangular piece is connected to has a green light, which can somehow be activated to shine a bright light. The actual gun is connected to a cooling pack on the back of the suit, the pack not being seen in-game as Blue never turns around.
Also, a lever sticking out of the top of the suit, when pressed down, will activate Auto-Pilot Switch, which will move the suit without Blue controlling it. The Auto-Pilot Switch was not used at all throughout Test Subject Blue, even though the suit was designed for use with Blue. It is believed that there are other controls inside the cockpit of the suit, as Blue jumps out of the suit when he approaches a Food Pill, and it is believed this is done under his own control.The suit can probably also auto-repair itself from damage. During the game, blue often throws himself at the glass, causing it to crack. The Proto-Suit will then swipe over the cracks with a laser, and the damage will disappear.
The Proto-Suit appears in Nitrome Must Die, in the fourth boss battle. Blue attacks by firing blue proton bullets, increasing the rate of fire the lower his heath gets.
In Nitrome Must Die, he performs another type of attack, where he sticks his proton cannon in the air when he gains a point in Test Subject Arena. While doing this, he will release several large blue spheres that will rotate around and home in on the player. After Blue's max health is halved, he will transform into the Rex209.
- The suit may have been based on the Varia suit from the Metroid franchise.
- Rex209 has similarities with the Proto-Suit, possibly meaning Doctor Nastidous used Proto-Suit parts to make Rex.
- Blue may not like the suit because he cracks the screen when he is stationary.