
Profession Smith 6 ranks |

Let's see if I can draw a decent diagram...
...................DMD
WALL----------- -----------WALL
.....................P
PC (P on diagram) opens a door. Right on the other side is a Monster (M on diagram). EDIT: The monster is in the square right above the PC's.
Can the PC, on his turn, move diagonally to one of the squares marked D on the diagram? While technically NOT a corner, both sides of a doorway are pretty darned solid and I would think diagonal movement in this case would not be possible.
What's the general consensus?

Claxon |

Yes, but the player may need to use acrobatics to move through the enemy's square.
Without acrobatics...I'm not sure. Your diagram isn't super clear, but as I understand it you basically have a door with a monster behind it and wanting to move by the monster, into an adjacent square. At the very least you will provoke if you can make the move. But I'm pretty sure you can't move through a square that has an object filling it like that. Doesn't matter if you move diagonally or not.

DM Livgin |

You can't move diagonally past a corner (even by taking a 5-foot step). You can move diagonally past a creature, even an opponent.
Assuming I understand your question, you can not move diagonally through a corner.
EDIT: Oh, I see you mentioned corners already. Wall/corner, use your judgement.