Thanks to Pid.Bungie.Org's story page providing the demos (and the power of foreknowledge on how to use the blue crystal), I finally conquered the PID demo after some 20 years. Both of them. This is what I get for demo 1.0:
What? Over 30 levels? Bungie, you bunch of liars, the canon game only has 25! But wait——that's not all! they made a correction in the 2nd demo:
Closer, but still misleading. What was going on to make Bungie think there were more than 25 levels in their own game? Were they making cuts from the final product?