An extended look at the hole-in-the-wall from the CB Pictorial research. Previously unpublished for the fear of bug exploitation...

Pretty amazing stuff! Spells go through completely enclosed rooms.

And then again, there’s an even bigger surprise waiting just around the corner.

Now, when I stood right up against the corner, the Flamewave got its maximum spread. Notice the flame kinda went right through to the bottom where it is solid?

Side note: See? It’s on the side :) Flamewave gaps - Look at the last frame of the animation. The monsters left standing are evenly spaced out - every other row perpendicular to the wave, at least according to this cast. Need more testing to see if it hold true in all cases and if it has the same effect with a straight cast. See addendum for more.

Firewall - Now, this gets a bit more powerful yet, as far as low lvl chars and church are concerned. You can cast firewalls through these holes in the wall.

The still and animation show not only can you cast over the wall at the diagonal, you can cast it parallel to the wall (a surprise to me). However, I was not successful at casting it against the Southwest wall in this particular room.

Also note that I was standing on the second square and casting straight forward in this animation. So much for the Line-of-Sight requirement.

A CAN OF WORMS - Recognizable patterns of holes-in-the-wall in the catacombs (and maybe hell) and invisible walls in hell. - the D filez II and D filez III

Addendum

Flamewave - casting directions = 8 After much testing, it is confirmed that Flamewave has blind spots also. This only happens when one is casting at a diagonal angle - on straight casts, I was getting 100% hits on monsters. With a diagonal cast, every other rows (red potions), for the entire path of the flame are blind spots. All the tests were consistent with the second animation of this page. That means only half of the monsters get hit.

There are 2 ways you can look at the rows of potions, vertically or horizontally to the screen orientation. The following observation pertains to the horizontal rows (same as the Flamewave orientation).
I am not sure if this is the cause of the blind spots, but... Each flame graphic (of the wave) loops from small to big and again throughout its travel. While studying this sequence of pictures, I noticed that the flame graphics reach their maximum width while on the blue rows and the smallest when they are on the red row, which enables the flames to pass in-between the reds (seemingly) without touching them.

Addendum II
After completing the Firewall guide - This makes for a better explanation of the Flamewave misses. Diablo game tiles are tilted 45 degrees to the right as shown below. For example, when casting a Firewall horizontally (yellow tiles) is actually a diagonal cast according to the game. If the warrior casts a Flamewave standing at 0,0 the wave would have a start position at 1,1 and travels down to 2,2 - 3,3 - 4,4 and so on - effectively missing every other rows.

Continue to
D filez II - Invisible Walls in the Butcher’s room and Hell
D filez III - Holes in the Catacombs and Hell, and staircase, umm, a case of stairs ;p