Dr. Reflex appears as a poorly clay-modeled humanoid character that resembles a rag doll with brown hair styled as a ponytail, a long nose, four fingers on each hand, realistic blue eyes and a red-lipped mouth with two buckteeth 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 a 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 up 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.