Not so simple

nice design and hidden zapper

There is one thing that is a bit strange for me. When B goes down the stairs fast, it gets an electrical spark. But when it's done a little slowly , it sometimes lucky to survive.

Spoiler: Down the stairs

To get down the stairs without getting zapped tap on the bottom of the stairs once B is between the first and second stair use the cancel button to stop him. The important thing to consider here is B should be between first and second stair. If you have done that correctly tap on the bottom of stair and B will get down without getting zapped. And this works all the time.

@DEVIL That's the explanation I was looking for
thank's

Yeah booiiiiiiiii....!!!
It was tough

But completed it!!!!!