Turning Opacity into Collision

Hello, what I am currently trying to achieve is using opacity masks to dictate what parts of an object have collision. In the screenshot example, the black slope selected is actually a square plane with a material applied - I want it so that the character can walk up and down the slope, rather than standing on top of the plane’s collision. Any advice would be greatly appreciated

P.S. I know that I could use Paper 2D in this specific example but I want to be able to do it with 3D objects as well.