Hey, guys, I have been scouring the lands for information on how changing size (i.e. Enlarge Person) affects your surroundings (specifically adjacent moveable items).
For example, let's say my Draconic Sorcerer wants to use Form of the Dragon III to change into a Huge Green Dragon and he has a barrel to his left, an ally behind, and enemies to his right and in front. A medium creature takes up a single 5 ft. square, whereas a huge creature takes up 15 ft. What happens to the objects/creatures adjacent to my medium character when he becomes huge? Do they simply get pushed out of the way? Do I make a Strength, Reposition, or perhaps a Bull Rush check on each of the affected objects/creatures? What if there is a wall or drop-off between me and the item(s) in question?
This is not specifically addressed in the polymorph rules for some reason, so I would probably steal this rule:
If insufficient room is available for the desired growth, the creature attains the maximum possible size and may make a Strength check (using its increased Strength) to burst any enclosures in the process. If it fails, it is constrained without harm by the materials enclosing it—the spell cannot be used to crush a creature by increasing its size.
So pushing anything out of the way is a Str check at your increased Str to "burst the enclosure." If you fail to push them out of the way on both sides, you end up being less than Huge, "constrained without harm by the materials."
To anticipate the next question, if you end up less than Huge due to constraints, what happens when those constraints are removed? Do you now finish growing? The answer is clearly the same as happens with enlarge person. What that is is less clear, but I think you do finish growing when possible.