Reflex

Reflex is the first character to appear in The Backroom, and as such gets top billing on the title screen and in promotional material. He also appears as Santabot in the Christmas Edition.

The Backroom (Original):
In the Backroom, Reflex is very robotic in appearance compared to the other characters. He has a pale grayish face, with two red eyes surrounded by maroon markings. Reflex's mouth is jawless, and as a result, the teeth are attached to the face. Inside the mouth, heat can be seen in the interior. Wrinkles surround both the upper and lower parts of the mouth. The torso is also maroon, with the areas up to the elbow attached. The forearms are colored gray and the hands (resembling gauntlets) are maroon. He has a grey waist. Attached to that waist, the pelvic and thigh regions are fused to each other and are maroon. The lower leg region is grey and the feet (which resemble boots) are maroon.

The Backroom: Christmas Edition:
In Christmas Edition, Reflex has been re-skinned as Santabot. Santabot's body now resembles a Santa suit, and the head has been recolored to also resemble Santa, albeit without the iconic beard. A hat also appears above Santabot's head.

The Backroom II: Retribution:
In Retribution, Reflex's body is very similar to that of the original reflex, albeit de-saturated. The main difference is in the face, which is much less round and having parts of the middle of the face absent all-together. More wrinkles are also present, and the existing ones have grown larger.

Personality
In the Backroom and Christmas edition, Reflex does not have an evident personality. In Retribution on the other hand, Reflex is shown to have limited to no emotional capability.

However, this could simply be role-playing.

Gameplay
Reflex's gameplay is the most iconic element of the Backroom games, and is notorious for being unbelievably frustrating.

The Backroom
Reflex first appears at the beginning of the night, and he has two modes, inactive and active. When inactive, do not press space, as that will automatically disturb him, resulting in a jumpscare. When active, press space as quickly as possible, as when Reflex is active, he is ready to jump-scare you.

When activated by the Doctor, the player has less time than normal to deactivate Reflex.

The Backroom: Christmas Edition
Same as the Backroom, though there is a little more time to press space.

When activated by the Silver Bell, the player has less time than normal to deactivate Santabot.

The Backroom: Retribution
The core of Reflex's game-play is the same, though there is a distinct differences, mainly that Reflex is active for longer, giving the player more time to deactivate him.

Trivia

 * Reflex was partially inspired by Nightmare Balloon Boy in ultimate custom night, particularly in the mechanics.
 * When speaking, Reflex voice gets slower and deeper with each passing word.
 * Reflex was named after his mechanics, which are heavily reliant on the player's reflexes.