Mannequin_Mark has an entirely wooden body, except for his 'legs', which is a dark gray stand. It has a crudely drawn face that is similar to the default Roblox face and wears a hard hat that can be red, orange, yellow, light green, dark green, cyan, blue, hot pink, or white.

In his Halloween 2023 appearance, his wood is dark-cyan in color. [2]

In his Christmas 2023 appearance, he is wearing reindeer antlers and a big red nose.

In its 2024 April Ghouls' Update, it has the appearance of glevil. Mannequin_Mark is usually a friendly, well-meaning construction worker. They mostly talk about wood and woodworking, with them having a general dislike for all other building materials. They can also be extremely stubborn when it comes to construction material, praising wood above everything else. They specifically dislike concrete to the point of violence against players who drink Wet Cement in front of him. Due to his tastes in building materials, he and Wallter don't get along, and are often hostile in their interactions. Despite this, it is hinted that Mark still loves Wallter despite his preference for concrete.  

Mannequin_Mark spawns through Stanley's Office floor, where the ceiling of the first room will collapse, with him falling through the now broken roof and saying "Hey Jim." Afterwards, Mark will hop into the elevator, unless the elevator is full or MR is in the elevator. Mannequin_Mark will exit the elevator on the Backrooms, Slide 4 Admin, Shop Space, Skyblock, Random Maze, Tumblr Ballpit and Cardboard Mansion floors.

Upon entering the elevator for the first time, they give everyone (including NPCs) a hardhat of varying color (red, orange, yellow, light green, dark green, cyan, blue, hot pink, or white), alongside the hat's intrinsic Effects (immunity to Spike).

Mannequin_Mark will punch the player once if they have Cemented! effect from drinking Wet Cement, or if they drink it in front of him. His punches deal 5 damage and -5x effect to the player. They will also refuse all attempts to give them Wet Cement.

https://regretevator.fandom.com/wiki/Mannequin_Mark - His wiki!

I hear Mannequin Mark's voice sort of like the average old-guy working at the office!
Give it your best take! (Im thinking of Mr Krabs)