You can move through a hex occupied by a friendly character, unless you are performing a Move By or a Move Through. When you move through a hex occupied by a friendly character, that character doesn't provide you with concealment.
You can't move through a hex occupied by an opponent who is not helpless (for example, unconscious or paralysed) unless you make a successful Acrobatics skill check or the opponent is the target of your Move Through. You can move through a hex occupied by a helpless opponent without penalty. Some characters, particularly very large ones, may present an obstacle even when helpless. In such cases, each hex you move through counts as 2 hexes. You can't end your movement in the same hex as an unfriendly character unless it is helpless.
Very small characters with at least two levels of shrinking can move into or through an occupied hex. The character provokes attacks of opportunity when doing so.
Any character can move through a hex occupied by a very large character at least three Growths larger than it is. Conversely, a big character can move through a hex occupied by a very small character three Shrinks smaller than it is.
Note that some characters break the above rules. A character that completely fills the hexes it occupies cannot be moved past, even with Acrobatics or similar special abilities.
Difficult terrain hampers movement. Each hex of difficult terrain counts as 2 hexes of movement. If you occupy hexes with different kinds of terrain, you can move only as fast as the most difficult terrain you occupy will allow. Flying and desolidified characters are not hampered by difficult terrain.
Like difficult terrain, obstacles can hamper movement. If an obstacle hampers movement but doesn't completely block it each obstructed hex or obstacle between hexes counts as 2 hexes of movement. You must pay this cost to cross the barrier, in addition to the cost to move into the hex on the other side. If you don't have sufficient movement to cross the barrier and move into the hex on the other side, you can't cross the barrier. Some obstacles may also require an Acrobatics skill check to cross. On the other hand, some obstacles block movement entirely. A character can't move through a blocking obstacle. Flying and desolidified characters can avoid most obstacles.
In some cases, you may have to squeeze into or through an area that isn't as wide as the space you take up. You can squeeze through or into a space that is at least half as wide as your normal space. Each move into or through a narrow space counts as if it were 2 hexes, and while squeezed in a narrow space you take a -2 penalty to OCV and DCV. When a character with a level of Growth (which normally takes up a two-hex radius) squeezes into a space that's one hex wide, the character's miniature figure occupies two hexes, centred on the line between the two hexes. For a bigger character, centre the character likewise in the area it squeezes into. A character can squeeze past an opponent while moving but it can't end its movement in an occupied hex.
To squeeze through or into a space less than half your space's width, you must use the Contortionist skill. You can't attack while using the Contortionist skill to squeeze through or into a narrow space, and your DCV is reduced to 0.
Sometimes a character ends its movement while moving through a hex where it's not allowed to stop. When that happens, you stop in the last legal position you occupied, or the closest legal position, if there's a legal position that's closer.
When your movement is hampered in some way, your movement usually costs double. For example, each hex of movement through difficult terrain counts as 2 hexes. If movement cost is doubled twice, then each hex counts as 4 hexes. If movement cost is doubled three times, then each hex counts as 8 hexes and so on.
Despite penalties to movement, you can take a full-round action to move 1 hex in any direction. (This rule doesn't allow you to move through impassable terrain or to move when all movement is prohibited.) Such movement provokes attacks of opportunity as normal (despite the distance covered, this move isn't a 1-hex step).
Characters with more than two levels of Shrinking or with one or more levels of Growth have special rules relating to position.
Very small characters take up less than 1 hex of space. This means that more than one such character can fit into a single hex, even if they are opponents. Four characters with two levels of Shrinking can fit into a single hex. Twenty-five characters with three levels of Shrinking or 100 characters with four levels of Shrinking can fit into a single hex.
Characters that take up less than 1 hex of space typically have no natural reach, meaning they can't reach into adjacent hexes. They must enter an opponent's hex to attack in melee. This provokes an attack of opportunity from the opponent. You can attack into your own hex if you need to, so you can attack such characters normally. Since they have no natural reach, they do not threaten the hexes around them. You can move past them without provoking attacks of opportunity.
Very large characters take up more than 1 hex. Characters that take up more than 1 hex typically have a natural reach of 2 hexes or more, meaning that they can reach targets even if they aren't in adjacent hexes.
Targets which are partly Concealed or "behind cover" are harder to hit. If a target is half Concealed (like a person behind a table or leaning around a corner), the target has a +2 DCV bonus. If the target is mostly Concealed (like a person peering out a door), the target has a +4 DCV bonus. In addition, you can't execute an attack of opportunity against an opponent with any degree of Concealment relative to you.
To determine whether your target has Concealment against your ranged attack, choose a corner of your hex. If any line from this corner to any corner of the target's hex passes through a hex or border that blocks line of effect or provides cover, or through a hex occupied by a character, the target is half Concealed.
When making a melee attack against an adjacent target, your target is half Concealed if any line from your hex to the target's hex goes through a wall (including a low wall). When making a melee attack against a target that isn't adjacent to you (such as with Stretching), use the rules for determining Concealment against ranged attacks.
A low obstacle (such as a wall no higher than half your height) provides Concealment, but only to characters within 6 hexes of it. The attacker can ignore the effect of the wall if he's closer to the obstacle than his target.
Any character with at least one level of Growth determines Concealment against melee attacks slightly differently. Such characters can choose any hex that they occupy to determine if an opponent has Concealment against their melee attacks. Similarly, when making a melee attack against such characters, you can pick any of the hexes it occupies to determine if it has Concealment against you.
If you don't have line of sight to your target they have total Concealment from you. You can't make an attack against a target that has total Concealment.
You can't execute an attack of opportunity against an opponent with total Concealment, even if you know what hex or hexes the opponent occupies.