It is not actually 3d, but as far as I know, there is no other working "3d" engines for scratch 1.0.0, at most, maybe slow raytracing. With this, most of the script would be in each sprite. Move with the arrow keys, and look around with w,a,s,d, to return to a neutral up or down state, press w and s at the same time, (remember I made this engine in scratch 1.0.0). I know there are still a few bugs, I do hope to improve it someday. To use this in Scratch 1.0.0 (You can use this engine for any project as long as you give me credit on the side, you do not have to remix this) here is the engine.sb download: https://archive.org/details/engine_202010
To upload this, I had to load it (the .sb file) in scratch 2.0, and save as .sb2, then I had to open that with scratch 3.0 online.