The September Previews page includes the Sovereign Beast epic destiny, which allows you to grow to Large size when Wild Shaping. It also includes an at-will power that allows you push adjacent enemies one square automatically that is triggered whenever you become Large in this way. An interesting effect, although it raises some interesting questions. I have my suspicions, but I am curious as to what others think.
First, the pushing power is a free action rather than an immediate reaction or immediate interrupt, so I am not sure whether it is supposed to happen before, after, or at the same time as the growth. Anyone know any rulings related to this issue?
Second, if you have enemies flanking you along a non-diagonal, are you incapable of becoming Large because there is no room to do so? If you can, what happens?
Third, if the answer to #2 was no, then once you have the push effect, are you then capable of growing since you will be pushing the enemies out of the way, thus giving yourself room?
Fourth, if the answer to #3 was yes, if the enemies have terrain hazards behind them, does that change anything? What if there are walls behind them?
Quaestor the Wanderer
The September Previews page includes the Sovereign Beast epic destiny, which allows you to grow to Large size when Wild Shaping. It also includes an at-will power that allows you push adjacent enemies one square automatically that is triggered whenever you become Large in this way. An interesting effect, although it raises some interesting questions. I have my suspicions, but I am curious as to what others think.
First, the pushing power is a free action rather than an immediate reaction or immediate interrupt, so I am not sure whether it is supposed to happen before, after, or at the same time as the growth. Anyone know any rulings related to this issue?
Second, if you have enemies flanking you along a non-diagonal, are you incapable of becoming Large because there is no room to do so? If you can, what happens?
Third, if the answer to #2 was no, then once you have the push effect, are you then capable of growing since you will be pushing the enemies out of the way, thus giving yourself room?
Fourth, if the answer to #3 was yes, if the enemies have terrain hazards behind them, does that change anything? What if there are walls behind them?
Quaestor the Wanderer
PHB2 rules (under polymorph) that if you can't fit in the squares when growing larger, the polymorph stops and you are stunned for a round.
The power seems designed to push enemies out of the way so you can grow unhindered and should be timed immediately before the grow- "immediate actions" powers can't work on your own turn, so that's why they used free action. If an enemy is pushed into _EDIT Yes I meant Hindering difficult terrain and makes the save, he's knocked prone- I believe you can cohabit an enemy's space when it is prone (but I'd need to check the entry under prone in PHB1). If walls prevent the pushing, then it's likely the same as if you tried to grow in a tiny square- the polymorph cancels and you become stunned.
If an enemy is pushed into difficult terrain and makes the save, he's knocked prone-
One small correction: If you push an enemy into hindering terrain it can save and be prone. You can push into difficult terrain willy nilly no problem. A small but important dintinction. 
If an enemy is pushed into difficult terrain and makes the save, he's knocked prone-
As been mentioned, i think you mean hindering terrain.
I believe you can cohabit an enemy's space when it is prone (but I'd need to check the entry under prone in PHB1).
Only if the enemy is helpless.