I was reading some threads and saw information about pulling, stated as fact, which I know is wrong. So I thought Id write my experiences down, and pass them on. These are how things seem to work for me. They may be wrong. They may be outdated. So take it with a grain of salt. Just trying to pass on what I think Ive learned about pulling in this game.
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Some Definitions:
Aggro Radius - The distance between you and the foe required for it to initially sense you. Radius varies by from foe-to-foe and by Line of Sight.
Attack Range - The maximum distance at which a foe can attack you.
Broadcast Radius - The range one foe can broadcast an alert to another foe.
Line of Sight - The forward angle in which a typical foe can "see".
Roleplaying Linkage - Some foes are linked by the encounter they are in, which can affect how they react to players.
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OK, now that some definitions are out of the way, lets look at how a foe can become aware of your presence.
1 ) You get close enough that it can see you if its facing you, or sense you if its facing away from you. Example: You run up to a foe. You usually have more room to work with, if you run up behind it.
2 ) You perform an action against the foe. Example: You shoot it or taunt it.
3 ) A second foe broadcasts an alert to it, because that second foe has been attacked. Example: You shoot the foe closest to you, and it squawks to its buddies that it is in combat.
4 ) A second foe broadcasts an alert to it, because that second foe is attacking you. Example: A foe draws its pistol and shoots at you, and warns all his nearby buddies that he is in combat.
Numbers 3 and 4 seem to have different radius, with 4 being noticeably larger. You can sometimes get away with pulls violating 3, if they don't violate 4.
5 ) A leader/spotter foe broadcasts an alert to it, because the leader/spotter senses or sees you. Example: A boss senses you and says something like Ice that sucker!, and before you are even in combat, he warns all the minions around him that a hero is nearby.
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So what does this mean about pulling?
A ) Know your enemy. Are the minions smart (Reapers) or dumb (zombies)? Do the leaders broadcast alerts when they sense you, or only when in combat. Are the foes linked for roleplay reason?
B ) Most Lts and Bosses send out alerts even if they are not in combat. It is very difficult to pull single Lts or Bosses away from their minions for this reason. It is usually easier to pull minions away from other minions (or minions away from leaders, if the leaders aren't looking).
C ) It is considerably easier to pull a foe away from the herd, if the rest of the herd is facing away from your target. In other words, get the guy at the back of the group. If theyre tightly packed and facing in all directions, your chance of success is very slim.
D ) It is very difficult to pull singles from a tightly packed herd with an attack. See #3 above. There are however some exceptions. Sniper blasts are good at this. I think Taunt is good at this. Teleport Foe is NOT good at this.
E ) If you successfully get the attention of a single foe, you must make sure that it can NOT attack you until it is far enough away from its buddies. Otherwise, it will broadcast to them that it is attacking someone. See #4 above. This is a classic way that pulls go bad. You successfully sniper or taunt a foe, it runs 20 feet from its friends, then stops and whips out a gun and blows the pull.
There are a couple ways to deal with this situation: stay out of range, so the foe has to move completely away from his friends before he can use a ranged attack OR duck around an obstacle so that the foe has to come to you to attack.
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Specific powers in relation to pulling:
Sniper: Sniper is a category of blast powers useable by Blasters and Defenders. It seems to have a significantly reduced chance of alerting nearby foes that their friend is in combat. When combined with good range, this often allows Blasters and Defenders to pull singles. It is very important to make sure that your target can not return fire while he is still anywhere near his buddies.
Taunt: See Sniper. It seems to also have a reduced chance of notifying nearby foes, but correct me if Im wrong, because I havent tested it much.
Teleport Foe: The AI seems to consider TP Foe an attack. Your target broadcasts a small-radius alert to all around him that he is under attack and in combat whenever you try to use this power. It can still be successful, if the herd is not too tightly packed. But under most circumstances, this will NOT pull singles from a tightly grouped herd.
So why do people consider this a good pulling tool (other than the obvious tactic of TP them to somewhere his friends cant follow)? Because of #4 above. By immediately getting a foe away from his friends, his return fire can not warn his buddies. This means that this power is actually sort of handy if the foes are near each other but not tightly packed, like is often the case in warehouse missions. A short-range alert goes out when you try to use TP Foe, but the alert that goes out when it returns fire seems to be larger and more dangerous. TP Foe can eliminate that second alert by getting the foe far away from others, or around a corner.
Provoke: Is an area effect, and thus usually bad for trying to pull singles.
Stealth (and other stealth-like powers): Allows you to get closer and use terrain better. This basically allows you to pull with a non-ranged attack, IF you can avoid return fire until the foe is away from his buddies. This can often be achieved in missions, where you pop around a corner and smack a foe with a fast attack, then pop back around the corner and get some distance. If the foe cant return fire until hes put a wall between him and his friends, you can be successful.
Movement Powers: Many movement powers can help you in pulling by preventing return fire. SuperSpeed is the one I have the most experience with. It has a stealth component, so you can often get close enough to pull with an attack, but then get away fast enough to prevent return fire until the foe is separated from his buddies.
Summary: Pull minions. Pull the minion that no one is looking at. Pull with Taunt or Sniper, (as opposed to an attack, Teleport Foe, or Provoke). Make sure that the minion cant attack you until its far enough away from his buddies.
If you dont have Sniper or Taunt, you can pull by being seen or sensed by one foe, IF you make sure that he cant attack you until hes away from his buddies (e.g., play peek-a-boo around a corner/obstacle).
If you pull with an Attack or TP Foe (instead of Sniper or Taunt), then there needs to be more space between foes, to avoid the short-radius alert. However, this can still be handy, if you can avoid return fire until the foe is away from his buddies or has a wall between him and them.
Anyway, those are my thoughts on the matter. They may well be all wrong, but sopme of it should be correct and useful to those new to the game. Please post corrections, if I've messed up anything. In particular, I haven't used Taunt much.