Three-Dimensional Platformer Tech Demo.
Programmer3000: Download the CAPX and find out! It’s made with some paid edition features, but I’m pretty sure you can still look at the events. I’ll try to summarize it in one comment:
Every object has x, y, and z coordinates, and the camera rotates horizontally and vertically. Based on the current camera angle, trigonometry translates the 3-D coordinates into an x,y position on the screen. The terrain sprites’ animation and frame are set based on the camera angle. Everything stacks back to front, bottom to top to put the right things in front of each other. Collision is based on position.