Though the Melee Reach rules are pretty clear (melee attacks by creatures with the Melee Reach ability use the ranged cover rules), people are often confused about whether an enemy has cover versus an attacker with Melee Reach. These diagrams attempt to explain the rules in a visual way.
As I mentioned, melee attacks by creatures with the Melee Reach ability use the ranged cover rule from page 17 of the Aberrations rulebook:
"Determining Cover: To determine whether a creature has cover from a ranged attack, the player who controls the attacking creature chooses a corner of a square in the attacking creature's space. If any line traced from this point to any part of the target's space passes through a wall or through a square or border that provides cover, the target has cover. (In practice, the attacker tries to find a corner that allows an attack without giving the defender cover.)
Touching Edges: The target does not have cover if the line runs along or merely touches the edge of a wall or other square that would otherwise provide cover."
Scenario A: Does the Dwarf have cover versus the Minotaur?
No. If the Minotaur chooses its middle-right corner, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover. Therefore, the Dwarf doesn't have cover versus the Minotaur's melee attack.
This is the obvious case that most people already know how to handle. It just shows how to apply the rules for determining cover versus an attacker with Melee Reach.
Note that the Minotaur isn't limited to choosing just its middle-right corner:
If the Minotaur chooses either its top-right or bottom-right corners, it would also be able to attack the Dwarf without cover. There are often multiple corners an attacker can choose which will prevent the target from having cover.
Scenario B: Does the Dwarf have cover versus the Minotaur when another creature is in the way?
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the Dwarf's space without crossing the Orc's space. Therefore, the Dwarf has cover versus the Minotaur's melee attack.
Even if the Minotaur chooses its bottom-right corner, the Dwarf still has cover:
Though the Minotaur can trace unblocked lines from its bottom-right corner to some parts of the Dwarf's space, that's not enough. The Minotaur has to be able to trace unblocked lines to all parts of the Dwarf's space in order to prevent the Dwarf from having cover.
Note that it doesn't matter whether the other creature is an enemy or an ally. All creatures provide cover equally in these situations.
Scenario C: Does the Dwarf have cover versus the Minotaur when a statue is in the way?
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the Dwarf's space without crossing the statue's space. Therefore, the Dwarf has cover versus the Minotaur's melee attack.
This is really the same situation as Scenario B. Statues provide cover versus Melee Reach attacks the same way creatures do.
Scenario D: Does the Dwarf have cover versus the Minotaur when a wall is in the way?
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the Dwarf's space without crossing the wall. Therefore, the Dwarf has cover versus the Minotaur's melee attack.
This is really the same situation as Scenario B. Walls provide cover versus Melee Reach attacks the same way creatures and statues do.
The Minotaur isn't limited to choosing its bottom-right corner:
Even though there is obviously a wall in the way of its top-right or middle-right corners, the Minotaur could still choose to use either one of those corners (or any other corner in its space for that matter) if it wanted to. It doesn't help in this situation, though. Choosing either of those other corners still provides the Dwarf with cover.
Scenario E: Does the Dwarf have cover versus the Minotaur when a thin wall is in the way? (Configuration 1)
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the Dwarf's space without crossing the wall. Therefore, the Dwarf has cover versus the Minotaur's melee attack.
Scenario F: Does the Dwarf have cover versus the Minotaur when a thin wall is in the way? (Configuration 2)
No. If the Minotaur chooses its bottom-right corner, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover. Therefore, the Dwarf doesn't have cover versus the Minotaur's melee attack.
The Minotaur can also avoid cover if it chooses its middle-right corner:
Note that all of the lines from the Minotaur's middle-right corner do touch the very end of the wall, but touching a wall isn't enough to provide cover; a traced line must cross a wall to provide cover.
However, the Minotaur can't avoid cover if it chooses its top-right corner:
Even though the lines from the Minotaur's top-right corner only touch one point of the wall, this counts as crossing the wall, and therefore the Dwarf would have cover if the Minotaur chose that point. If you trace a line to determine cover from a creature on one side of a wall to a creature on the other side of the wall, and the line originates at a non-endpoint of the wall, the line counts as having crossed the wall. (This isn't in the rules yet, but it's the way the rules are supposed to work.)
Scenario G: Does the Dwarf have cover versus the Minotaur when a variety of walls, creatures, and statues are around him?
No. If the Minotaur chooses its top-right or middle-right corner, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover. Therefore, the Dwarf doesn't have cover versus the Minotaur's melee attack.
Note that all of the lines from the Minotaur's chosen corner touch either the Orc's square or the Statue's square (at the origin point at the very least), and some of the lines touch the wall and/or the Gold Champ's square, but touching those things isn't enough to provide cover; a traced line must cross a wall, creature, or statue to provide cover.
Scenario H: Does either Dwarf have cover versus the Minotaur when a variety of walls, creatures, and statues are in the area? (Configuration 1)
No, neither Dwarf has cover. If the Minotaur chooses its top-right corner when attacking the upper Dwarf, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover. Therefore, the Dwarf doesn't have cover versus the Minotaur's melee attack. Similarly, if the Minotaur chooses its bottom-right corner when attacking the lower Dwarf, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover.
Note that all of the lines from the Minotaur's chosen corner touch various other creatures', statues', or walls' squares (at the origin point at the very least), but touching those things isn't enough to provide cover; a traced line must cross a wall, creature, or statue to provide cover.
Scenario I: Does the Dwarf have cover versus the Minotaur when a variety of walls, creatures, and statues are in the area? (Configuration 2)
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the Dwarf's space without crossing either the statue or the Orc. Therefore, the Dwarf has cover versus the Minotaur's melee attack.
Even choosing the middle-right or lower-right corner doesn't help.
Scenario J: Does the adjacent Dwarf have cover versus the Minotaur?
No. If the Minotaur chooses its top-right corner, it can trace a line from there to all parts of the Dwarf's space without crossing anything that provides cover. Therefore, the Dwarf doesn't have cover versus the Minotaur's melee attack.
Note that we're using the ranged cover rules against an adjacent enemy; the Melee Reach rules work against all enemies, even those who are adjacent.
This is what makes Melee Reach so powerful. Though the Dwarf doesn't have cover versus the Minotaur's melee attack, the Minotaur does have cover versus the Dwarf's melee attack:
Because the Dwarf doesn't have Melee Reach, the Dwarf uses the normal melee cover rules when making melee attacks against other creatures. (These are described in the Cover in Melee diagram on page 13 of the Aberrations rulebook.) This gives the Minotaur (or any other creature with Melee Reach) a big advantage when fighting at a corner with a creature that doesn't have Melee Reach.
Another cool aspect of this situation is that the Minotaur is in a position to take more attacks of opporunity than a normal (non-Melee Reach) creature would be able to:
Because the Minotaur threatens the Dwarf's square, and because the Dwarf doesn't have cover versus the Minotaur's melee attack, the Dwarf provokes an attack of opportunity if it moves.
Even better, the Minotaur can move without provoking an attack of opportunity from the Dwarf:
Even though the Dwarf threatens the Minotaur's square, the Minotaur has cover versus the Dwarf's melee attack. Therefore, the Minotaur can move out of that square without provoking an attack of opportunity from the Dwarf.
Scenario K: Do the various adjacent enemies have cover versus the Minotaur?
No. In each case, the Minotaur can trace a line from a corner of its space to all parts of the enemy's space without crossing anything that provides cover. Therefore, none of the enemies have cover versus the Minotaur's melee attack.
Scenario L: Does the large enemy have cover versus the Minotaur when an Orc is in the way?
Yes. Regardless of which corner the Minotaur chooses, it cannot trace a line from the chosen corner to all parts of the large enemy's space without crossing the Orc's space. Therefore, the large enemy has cover versus the Minotaur's melee attack.
The important thing to note here is that the Minotaur must be able to trace unblocked lines to all parts (ie. all squares) of a large creature's space in order to prevent the large creature from having cover. It's not enough for the Minotaur to be able to trace unblocked lines to just one square in the large enemy's space.
Similarly, when making a Melee Reach attack against a huge enemy, the attacker must be able to trace unblocked lines to all nine squares in the huge creature's space. Here, the huge enemy has cover versus the Minotaur's melee attack because the Minotaur cannot trace a line from the chosen corner to all parts of the huge enemy's space without crossing the Orc's space.
More Examples
In the above situation, a LG warband comprised of two dwarves, two gnomes, a Purple Dragon Knight (PDK) and a Gold Champion fights a CE warband made up of an Ogre with Melee Reach and four Orcs. The LG creatures are colored yellow and the CE creatures are greenish. The battle grid is represented by the gray lines, and walls are represented by black lines.
Scenario One: Does the Gold Champion have cover versus the Ogre?
No. If the Ogre chooses either its bottom-left corner or bottom-middle corner, it can trace a line from there to all parts of the Gold Champ's space without crossing anything that provides cover. Therefore, the Gold Champ doesn't have cover versus the Ogre's melee attack.
Note that all of lines from the Ogre's chosen corner do touch the Orc's square (at the origin point at the very least) and some even touch the left-most gnome's square, but touching a creature isn't enough to provide cover; a traced line must cross a creature to provide cover.
Scenario Two: Does the bottom-most dwarf have cover versus the Ogre?
No. If the Ogre chooses any one of its bottom corners, it can trace a line from there to all parts of the dwarf's space without crossing anything that provides cover. Therefore, the bottom-most dwarf doesn't have cover versus the Ogre's melee attack.
Note that we're using the ranged cover rules against an adjacent enemy; the Melee Reach rules work against all enemies, even those who are adjacent.
Scenario Three: Does the top-most dwarf have cover versus the Ogre?
No. If the Ogre chooses either its top-left corner or top-middle corner, it can trace a line from there to all parts of the dwarf's space without crossing anything that provides cover. Therefore, the top-most dwarf doesn't have cover versus the Ogre's melee attack.
Note that all of lines from the Ogre's chosen corner do touch the wall (at the origin point at the very least), but touching a wall isn't enough to provide cover; a traced line must cross a wall to provide cover.
Note that we're using the ranged cover rules against an adjacent enemy; the Melee Reach rules work against all enemies, even those who are adjacent.
Scenario Four: Does the Purple Dragon Knight (PDK) have cover versus the Ogre?
No. If the Ogre chooses its top-right corner, it can trace a line from there to all parts of the PDK's space without crossing anything that provides cover. Therefore, the PDK doesn't have cover versus the Ogre's melee attack.
Note that all of lines from the Ogre's chosen corner do touch both Orcs' squares (at the origin point at the very least), but touching a creature isn't enough to provide cover; a traced line must cross a creature to provide cover.
Note that we're using the ranged cover rules against an adjacent enemy; the Melee Reach rules work against all enemies, even those who are adjacent.
Scenario Five: Do the gnomes have cover versus the Ogre?
Yes. Regardless of which corner the Ogre chooses or which gnome it attacks, it cannot trace a line from the chosen corner to all parts of the target's space without crossing an Orc's space. Therefore, both gnomes have cover versus the Ogre's melee attack.
Note that the Ogre doesn't have to choose its bottom-left corner when attacking the leftmost gnome. Unfortunately for the Ogre, its other corner choices don't eliminate the cover. For example, all of the lines from the Ogre's left-middle corner still cross the Orc's space:
Note that the Ogre doesn't even have to choose a corner that's near the target. The only requirement is that the corner be somewhere in the Ogre's space. It could choose the corner in the center of its space, or even its top-right corner. Despite the fact that the Ogre only has Melee Reach 2, it doesn't even matter if the target is more than two squares away from the chosen corner; the distance associated with Melee Reach is the maxmimum distance the target can be from the attacker, not from the attacker's chosen corner.
Choosing another corner won't help, though. Choosing its top-right corner, for example, crosses its own space, a wall, and the Orc, so the gnome still has cover. The gnome still gets just a +4 bonus to AC in this situation, however, because the number of sources of cover is irrelevant; a creature either has cover or doesn't.
