I was recently reading a blog entry by my friend Veneretio in which he explained how to cluster multiple creatures into a group when tanking. In his entry, found
here, he covers a scenario in which a creature is a caster or ranged
shooter. This type of creature will not normally run to the tank and in most cases needs to be silenced. He went on to explain
line of sight (LOS). When I read the following excerpt I felt that LOS deserved a bit more detail.
LOS pulling is shooting a mob and then running around a corner forcing them to follow you around that corner to get into range. This has the benefit of not forcing you to waste a lot of time back tracking and in most cases, it’ll cancel any spell being cast on you.
Johnny is in room A, which is connected via a hallway to room B. Room A is empty and room B has a creature in it. Line of sight pulling would mean using a ranged attack and luring the creature into the empty room for a cup of tea. The following illustration shows the layout of the immediate area.

As we can see above, Mr. Blue sees Mr. Monster. Mr. Blue throws a ninja star at Mr. Monster, making him very upset. Mr. Monster begins to cast a very powerful Fireball, but Mr. Blue runs back around the corner, breaking Mr. Monsters line of sight. Mr. Monster stops casting a Fireball since he can't find his target and runs around the corner, right into a big, fat Shield Slam.
A Real UnderstandingAll creatures have a center point. When you target a creature a small circle or reticule is created under their feet to show they are targeted. This is a good reference as to the creatures center point (large creatures typically have larger center points, i.e. devilsaur or adult dragonkin). Imagine a direct line from this center point to the center point of your character in-game. This is considered "line of sight." In most cases a creature cannot see behind itself, but they will turn around and chase their target when aggroed. The logic is that players and creatures must make and maintain eye contact with its target in most cases and with most spells or it interferes with their ability to target. Guess there's a little bit of sense thrown into the mix as well. Who knew?!
ConclusionSo line of sight works just like many other aspects of the game, in particular tanking. Creatures are aggravated, threaten to kill adventurers, and even require actually seeing their enemy before taking action. When I first started playing the game in 2004 I was shocked at how
realistic those aspects of the game were. Pretty intuitive system.