how would i go about to create a 3d effect in a 2d top down game.

General
1

Like the walls how would I create an effect that mimics a wall from the top perspective

2

If I remember correctly, you may be able to load a 3D mesh in the 2D world with a MeshInstance2D. If you have preloaded your mesh in your files (from somewhere else such as blender), then you can pop it in the “Mesh” property. If you don’t plan on using a 3D model, then it may be more of a question of art. I sadly cannot help you make or brainstorm perspective art as I am… absolute crap at anything in that caliber.
Also, there is a section dedicated for Help (named as such as well). I would suggest posting over there for future issues if you would like some more attention to your issues

Short

MeshInstance2D