I know it's not an easy concept to grasp but lately I've gotten some sort of fever… it's the urge to create 3D polygons in a 2D world.

I've tried to find resources online but, the internet isn't very good for that kind of stuff. So I would like someone with experience to show/help me make a 3D polygon on scratch. I want to be able to understand it, not just play copycat. So, it would be great if someone would help me out. Thanks.

Your question is not completely clear.
1) There are lots of programs in scratch 1.4 that make a projection of 3D into 2D. Is that what you mean 3D in a 2D world ?
2) Some of them are doing this for, e.g., cubes. Is a cube an example of a 3D polygon for you ?

I disagree there's loads of this sort of stuff on the internet. You just need to bite the bullet and read as much as you can until you do understand it. A good grounding in matrices helps.

I think one easy way to make a 3d thing is you use the script “forever {go to x:0 y:0, switch to costume1, stamp, change y by 2, stamp, change y by 2, switch to costume3, stamp, change y by 2,}” and so on. In the forever loop, you can add direction or movement so that you can turn the 3d figure and/or move it around which is pretty nice. The only thing is that the script gets pretty long…

I'll look around the internet more. But stamping like that isn't really 3D, and I couldn't make a triangle. I could only make rectangles.

Just created this project, which shows the equation for rotation in 2d. 3d is just one more dimension with the added complexity of projecting back into 2d.

right, that's what I've been trying to figure out. How to project the z axis. Thanks, I'll take a look

Here's one that does projection too. Just need to start mixing rotation, translations and projections to create a 3d engine

Well size growing when up arrow key clicked is the start