I've found what the "AI bound" refers to: it's the very first property of an item template (you can only edit it for templates, not for already instantiated objects). If it's not set, you can assign one. Unfortunately, it appears that the engine never allows walking on top of dynamically generated AI grids (even if WalkOn is checked for the object), so that's a dead end too (it does seem to override the lava AI grid if the object is high enough above the lava, so on that count it was okay).
Regarding you question of what I'm trying to do, "case study" would be the closest. I was trying to recreate
Frogger in the Divinity Engine, just to see whether I could
The idea of using triggers to create/remove lava is something I had thought of too, but the platforms are closer to how the game worked and indeed seem cooler. I already got the road/vehicles part of the game working, and that was surprisingly simple in the end: attach a charScript to every "vehicle" (animal in this case) that simply has a reaction when a player is within 1.0 distance of an animal (CharacterGet, CharacterIsPlayer), and if so kill the player (which was a bunny, since there is no frog model), wait half a second, transport him to the spawn trigger and resurrect him.
Since the platforms seem to be a no-go, I maybe I could go for Pac-man instead: after all, the above charScript would work equally well for the ghosts. For the pills/bullets that Pac-man has to eat, you could attach a similar script to the items representing them (moving them in Pac-man's inventory when triggered, rather than killing Pac-man), and also trigger an Osiris event when they're picked up so you can decrease a counter in order to detect when they've all been eaten
The pyramid mechanic you mentioned immediately reminded me of Portal, maybe that too could be recreated in some way
