At first he is seen as a pink figure as in the video, but after he gets electrocuted, he becomes a skeleton.
His name was revealed by his plush's product name.
His gender was revealed by his plush information.
Dummbkopf was named after his great grandfather, who enjoyed bomb disposal as a hobby. His name is German and roughly translated means someone who puts a fork in a toaster without pulling the plug out first. He is distantly related to Hapless, who also likes to prod dangerous things.
In the video
Dummkopf is seen holding a toaster with a fork right in front of him, and then lifts it up like in the picture above and gets electrocuted and his burnt flesh falls down, revealing his skeleton. He is a Second Dancer, just like Lax, Doofus and Mishap.
The player must carefully remove a piece of toast with a fork without touching the sides. If you fail, Dummkopf will get electrocuted. If you win, he will get his toast.
As part of the second update, he has a new game. This game requires you to prevent appliances from falling into the sink where he is washing dishes. If any of the appliances touch the sink, Dummkopf becomes a skeleton again, resulting in failure. If you win, he gets a piece of toast and eats it.