Quote Originally Posted by chaincomplex View Post
This interpretation is a little problematic because, for instance, imagine a ship with a prismatic wall sitting on its deck, facing towards the stern. The ship is moving at 1 mph. A person on the deck is walking to the aft at 1 mph. From the wall's perspective, the person is approaching it, and thus subject to its harm. From the world's perspective, the person is stationary, and the ship is moving the wall to the person.

I'm half considering letting you ram with the prismatic stronghold walls. Part of it is really that... anything that would be vulnerable to this, wasn't really going to be a threat to the party anyways. Plus presumably you wouldn't be typically be driving the schoolbus around in general adventuring per the principle of staying in the background here. I'll think about this more when the game gets going.
I think it's not just a matter of physics but intent. If you're falling and someone with an Antilife Shell moves between you and the earth, technically you're approaching them and thus the spell should trigger...but they're the ones who are forcing a confrontation between you and the edge of their abjuration. It's a weird edge case where, at least IMO, the spirit of the rules needs to shine through in rulings on any weird ambiguous situations.

If you're fine essentially ignoring the rule, or just saying that it doesn't really apply to prismatic wall specifically, I can definitely live with that.