Sorry for the late reply but yesterday I was visiting a comic convention.
About the rider, yes the rider is the angel of death. See below screenshot. Note I just put the rider in a random place I did not meet him here nor do I know how to meet him:

- cq_003.png (10.1 KiB) Viewed 14196 times
You have four turns before he leaves the room. He doesn't do anything, but you get killed if you examine him.
The code contains the words : assails nostrils rider's horse whoopsie. I guess something should happen to make the horse do its “whoopsie”
I thought maybe he is the shadowy figure behind the translucent wall in the cube room. But I don’t know how to remove the wall and if that is possible. (actually now if I think about it, I can remove the wall cheating. I'll give that a try and I will let you know)
Did the expert say something about solving the error with the zombie? The error has to be somewhere where the code checks if the sphere is in you possession and you pass the room with the zombie.
Concerning the web I tried a different approach. If you use CUT it says the web can’t be cut, If you try IGNITE is says the web can’t be lit.
EXAMINE WEB: You will need to clear it away to get past
If you try to CLEAR WEB with or without something you get too close to the web with one exception:
CLEAR WEB WITH SWORD
The web must be somewhat acidic as the sword dissolved on its first touch of the web.
We didn’t use the verb SPIN/TWIRL/ROLL yet. I was thinking should we cover the sword with something to protect it from the acid?