Dr. Reflex appears as a poorly clay-modeled humanoid character that resembles a rag doll with brown hair styled as a ponytail, a long upper jaw that extends into a large nose, four fingers on each hand, realistic blue eyes and a red-lipped mouth with two buck teeth in front of it. He wears a white shirt with black buttons, a gray stethoscope, black pants, light blue gloves, and brown shoes.

He has an energetic voice that seems to be randomly sped up or slowed down, with a sort of "warble" to it. While chasing the player, his voice will slowly raise in pitch until Dr. Reflex catches or loses track of them.

When he is enraged, Dr. Reflex grabs a large reflex hammer (which appears to be a large yellow percussion hammer with a gray handle) and holds it above his head with both of his hands. The reverb in his voice is amped up drastically while he is like this, giving a far creepier undertone to his voice. He also gets an orange tint.

Much like 1st Prize and The Test, Dr. Reflex has angled sprites, and as such he can be seen from various angles.

In his comic debut Dr. Reflex appeared as a human with an unusually elongated head (which mystman12 stated this was due to him running out of room while drawing Dr. Reflex) and, similar to his appearance in Baldi's Basics Plus, had buck teeth and a ponytail. In the original comic's last two panels he heavily resembled Baldi, just with thicker legs.

Dr. Reflex is eager to do his job as he will run toward the player when he sees them in order to initiate a reflex test. He gets upset when the player messes up the test, but is quite encouraging to them and wants them to try again. When his reflex test is interrupted for any reason, he will turn aggressive and attempt to hunt the player down with a percussion hammer.

Dr. Reflex first appears on floor 2 and spawns in his clinic. After spawning, he will wander around the halls in a unique fashion. Every time he reaches a destination, he will stop for one second, rotate towards the direction of the next destination, wait another second, and start going towards that destination. If Dr. Reflex spots the player with his peripheral vision, he will stop for more or less two seconds and look where he saw them. Once he sees the player, he will run after them and then start a reflex test upon full approach. If the player hides in a room or uses the Dirty Chalk Eraser to block Dr. Reflex's vision, he will ignore them. If they do not do that in time, he will start chasing after them.
Reflex test

Dr. Reflex's reflex test.

In Dr. Reflex's reflex test, the player will automatically turn to Dr. Reflex and he will wait a few seconds, then open his hands; one hand contains a circle and the other contains an X. To pass his reflex test and continue progressing, the player will need to click on the correct hand (the one with the circle) quickly enough, specifically within less than a second, hence his catchphrase he shouts before starting. When the player clicks on the correct hand without failure, they will earn 25 You Thought Points. However, Dr. Reflex will feel unhappy with the player if they are too slow or click the wrong hand (the one with the X), starting the challenge all over until the player wins.
Dr

Dr. Reflex squishes Baldi and Cloudy Copter with his percussion hammer.
Squished player

The player gets squished by Dr. Reflex's percussion hammer.

If the player simply walks away during his test, or even gets disrupted by any characters or specific items, he will get angry, wait two seconds, and head to his clinic to grab a giant percussion hammer and start hunting the player down. He will use it to squish any character (except for Chalkles) that he comes in contact with. The effect will last for 30 seconds. Like Baldi, Dr. Reflex is able to hear any and all noises that would normally alert Baldi, and likewise, using either the tape player or the pay phone will make him deaf for 30 seconds. However, unlike Baldi, there is no head indicator that shows whether Dr. Reflex heard a noise or not.

While being squished, characters' interaction will be limited. For example, the player will not be able to interact with some objects (such as buttons, notebooks and blue lockers) and other characters will not be able to interact with the player, such as Baldi, who will not be able to catch the player while squished. When the player is squished, their camera will snap towards Dr. Reflex, similar to the situation when he plays a reflex test.

After a while, squished characters will revert back to normal and interact normally again.

Unlike other characters who can see the player from all angles, Dr. Reflex will only be able to see the player as long as they are in front of him or in his peripheral vision.