Okay, we all know the white 'floor' or background to Mekorama - it's what gets built upon. And B can navigate the white floor if necessary, though usually it's only line of sight for him; he won't go around corners. However, there are some odd times - in the level "Elevate" by @sawdust , there are stairs leading down to the white floor... but B will not go up or down those stairs. Possibly it has something to do with the size of a level, or maybe not, but it does sound like something that needs to be explored.
That is interesting, and it makes sense, but it doesn't explain why you can't go up or down the stairs in "Elevate", unless I'm missing something.
It's a design-time exploit: When the boundary is reached that causes the Max World Size warning to pop up, any stairs that are placed at the boundary will be unscalable by B at play-time. And this effect persists even when the designer removes the blocks that are placed earliest - leaving a void behind what remains of the model. In my demo, Be My Guest (below, sorry for the messy scribbles), my first block was at position 1, then i placed blocks until positions 2 and 3 where Max World Size was reached. This established an invisible square boundary along which any stairs are unscalable by B at play-time. Then i built what you see in the model and erased the rest - exploiting the boundary along 5 and 6... Anyway in Elevate, @sawdust's stairs are like my stairs above - they were placed along a Max World Size boundary line (perhaps even establishing the boundary line at the time), followed by the removal of earlier blocks on the opposite side of the model. I hope this helps - I'm finding it surprisingly difficult to put into words! Come to think of it, you could probably do it in reverse: build your actual model (what you see in Be My Guest); and then add temporary blocks opposite the stairs that you wish to sabotage until you hit Max World Size; and then remove those temporary blocks. Much simpler to explain as well!
Okay, that explains some of it, but it still doesn't explain "Elevate" - B can't step outside the max world size, but he can be on the white floor at the bottom of those steps, so those steps were obviously never on the boundary.
@D.S.Masters - but B can step outside Max World Size Max World Size is a constraint on the designer (with certain repercussions later on the player).. But at play-time, B can walk all over the place, so can R, so can rolling balls.
