Dungeon Layout Bugs
All bugs in this category are related to problems with dungeon layouts, level transitions, the positions of objects, and other errors caused by the tile layout design of the game.
Screen Drae Errors in Caves
Certain wall formations in the caves can cause screen draw problems which are harmless. This is caused by spots on the level map that do not contain graphics, usually seen as stalagmites. Images in them will "ripple."
"Mirroring" effects can be seen where a character's image will appear in lava pools.
Level Resets
Occasionally, if you go down a set of stairs, back up, and back down again, the entire level changes. This includes wall placements, creatures, etc...which can lead to you arriving in the middle of a pack of monsters, or a wall.
Hell's Invisible Walls Sometimes in Hell levels, especially level 16, hidden walls exist which cannot be seen by the player but are treated as physical barriers that also block sight and shots. There seems to be a correlation between dead body parts hung on walls (aka "Shish Kebabs") and hidden wall squares.
Holes in The Wall
Many walls in the game have holes in them that allow arrows and spells to leak through. One such hole exists on the left side of Lazarus' chamber.
Impossible Levels
Very rarely will a level be generated that is not continuous - it is split into sides that can only be accessed by casting Phasing or Teleport.
ODar Off Map Aquares
Occasionally dotted map squares, corresponding to walls and inaccessible areas, will be visible on the map upon level entry - even when being very far away.
Monsters in Walls
Monsters will occasionally appear inside closed doors or walls, as they are generated there. As soon as they enter your light radius they simply walk out of the wall/door they were "in."
Ranged Attack Angels
Certain angles of ranged attack against monsters will result in a character being unable to hit them; the character will have to move a square to be able to score a hit. Shots fired in straight lines to the target are much easier to connect.
Sharing Squares
When a character teleports/phases onto a square that a monster was moving in to, they will overlap. The character will have to move off the square to hit the monster. The monster, however, can attack the same square it's standing on.
If two characters wind up occupying the same square, which can happen rarely when casting Teleport or when Resurrecting while standing over a body, the player who does not move will become invisible to both players, until he/she moves. Further, the player first on the internal list of players may be the first targeted and attacked if a monster approaches.
The player can also share a square with Golem
Stairway Problems
A character can teleport/phase into a stairway leading down in Hell levels and "levitate" in the open area inside the "cage" of the stairway. He/she can then shoot ranged attacks out of the mouth of the stairway, but no ranged attacks from monsters can get in from certain angles.
If you enter the caves via the cave mouth entrance near Wirt, you can run the mouse cursor over the stairs on level 9, and a small spot on the right side of the stairs will read "up to level 8." If you left click on that spot your character will begin walking towards the level 8 stairs (even if you can't see them on the map), unless the way is blocked by lava, grates, or some other obstacle. If you teleport onto that spot, your character will teleport all the way to the level 8 stairs and go up!
Players can "block" stairways when they enter them. A "ghost" image of the character remains at the stair entrance to the other players, and remains until the stair-taking player finishes loading up the next level. This blocking effect occurs 100% of the time when the player has a Mana Shield cast.
Monsters that use Hidden AI are always active. Unless there's a barrier between them and the player (e.g. closed door, barrels completely blocking a path), they'll reach the player without any action on the player's part.
The game normally doesn't generate monsters within a certain range of the stairs. This does not apply to rooms, however. For example, you may enter a level of the caves and find Storm Demons waiting 7 squares away, placed there because they are inside a fenced area. They will fire at you immediately, open the door, and come after you.
Boss Light Radii
All bosses in Diablo emit a light radius visible to players. If they move, their light radius moves as well. However, if you leave the level and re-enter, the bosses original positions will have a light radius on the floor, even when the boss' dead body is located at a different position on the level.
Level Enterance Displacement
When players use stairwells to go down, each player will see the other in the wrong spot at next level, with their player being in the "correct" position and the partner displaced. When the characters move, the game engine corrects this situation by showing the other player walk one space over.
In a similar fashion, a player taking another player's Town Portal down to a level can wind up on the other side of a wall if the portal was placed just to the "north" of the wall. This is due to a displacement of one square, as the player cannot land on the exact square of the Portal (they'd head right back up again, then).
Trap Reset
If a door with a trap is opened, thus setting off the trap, and the door is closed again, you can "reset" the trap. Leave the level and come back to it, and the trap will be reset.
127 Limit
You cannot drop more than 127 items on the floor in any one level, including town. Note that this can cause you to lose monster drops if you have 127 items on the floor of a level, since a dying monster will have no "room" to drop it and it will simply never exist. Remember that every pile of gold is an "item."
Diablo also has a 127 limit as to the number of ongoing spell effects (including arrows) that can appear on a level at any one time, which is 127. Some spells, especially Chain Lightning, can use up several effects.
Items Drops in Shrine/Bookcase Tiles
If an item drops on the tile for a shrine or bookcase, you cannot highlight or pick up the item until activating the shrine or bookcase.
Moonbender's Light Radius
The light square of Moonbender (a Blink boss) will freeze in place if it 'blinks' next to you, and won't follow the boss even if the boss moves afterward.
Unhittable When Walking Horizontally
When a character (or monster) walks horizontally on the screen (as in on your monitor), he/she/it cannot be hit by most spells and ALL arrows, even when fired on the same line of action of the walker.
Going Up and Down Stairs
You will only descend a stairwell while you're in "walk" mode. Other actions, such as swinging or casting, will prevent you from descending a staircase.