Inspired by this question, I wondered how this works in 3.5 edition. I did not find it in the Falling section of the Environmental hazards glossary in the DM's guide, is it covered somewhere? Should I assume it to be the same as in the following edition?
I’m not sure if it’s ever specifically addressed, but the 4e rule would work quite nicely in 3.5, and even in the absence of an explicit rule you could argue that the rules of 3.5 would work out the same: the creature isn’t able to fit all of its space on the grid because of the pit. It therefore must squeeze itself in the remaining squares.