Flanking Rules

When a creature and at least one of its allies are adjacent (within 5 feet) to an enemy and on opposite sides or corners of the enemy’s space, they are said to be flanking the enemy. The allies cannot be incapaciated in order to count towards the flanking. When a creature is flanked, all characters flanking that creature gain a +2 bonus to melee attacks. Adding an additional ally into the flank increases that bonus to +5 and they are now considered surrounded.

Flanked

Surrounded

This is still a surrounded NPC with +5 to all the flanking characters, including the one that just joined the group. There is no additional bonus towards the attack, but they count as being part of the flanking and also receive the bonus to attack.

Checking the Flank

In order for it to count towards flanking: draw a straight line between the allies. That line must by pass at least one of the NPC's squares close to the middle of the square.