Here is what I have noticed through playing and a lot of reading on various sites regrading mercs.
Level: When you purchase/hire a merc, it will be your level. As you level up (or level down), your merc will level up and down with you. When the merc levels up, it magically gets the spells/abilites for the next level without oever visiting a merchant. So the merc you buy at level 1 will stay with you until you are level 85 as long as you keep paying it.
Apprentice vs Journeyman: This designation affects a few things. Just consider an apprentice merc to be a casual group geared/spell/ability NPC. Consider a journeyman merc to be a serious group geared NPC. If "master mercs" are ever released, it is rumored that they be top end group/raid geared.
Apprentice mercs use rank I of spells. Journeyman are supposed to use rank II versions of the spells.
Confidence: This is a nice way of saying, "How bad does the situation need to be before my merc runs away?". First, whether you have an apprentice or journeyman merc will set the conditions to make the fleeing check. The check is based on the number of people in your group, level of people in the group, con of the mobs in the camp, number of mobs in the camp, how are you doing at getting the mobs under control, etc. So a journeyman merc will tolerate a more dire situation before the flee check is even made.
Ok, at this point, a flee check needs to be made. This is where the tier of the merc comes into play. Tier I merc flees 25% of the time when a check is made. Tier V merc flees 5% of the time when a check is made. So you might have the most cowardly merc (App T1), and as long as you don't overpull or have good CC, your merc will not make a flee check.
So your merc is fleeing. First, the merc steps out of aggro range and does nothing. The merc is actually giving you a chance to get things under control. If you get things under control the merc will actually come back and start doing it's role again. If you can't get things under control the merc runs away.
Accessing more Mercs: As you progress through SoD, more mercs will be made available. At first, App T1 to T5 and Jour T1 is available. I have read that gaining access to the Void B make Jour T2 available to that player.
DPS: I haven't done any parsing, but the I have read various items that says the more expensive the tank merc, the better their DPS is. A journeyman merc will do more dps than the apprentice (but this also follow the more expensive comment).
Gearing your Merc: You merc comes with gear. You cannot improve this. As you level and the merc levels, the merc's gear (through DPS, HP, AC) will magically improve.
Paying for your Merc: There are two costs related to the merc. I call them the the "signing bonus" and "salary". The signing bonus is a one time cost that you pay the merc merchant to get your merc. The salary is taken from your inventory cash every 15 minutes that the merc is active. No, you cannot suspend the merc right before the salary payment and re-activate after 15 minutes pass. The merc keeps an internal clock to make sure it gets paid.
If you don't have the cash in your inventory, the merc will acutally leave you. This means you'll need to pay the signing bonus again to get the merc back. If you are running low on cash, just suspend the merc until you get more cash.
Stances: Depending on the merc that you have, you may have more or less options available. All mercs have the passive stance which as mentioned above the merc does nothing. This can sort of be used like the "pet hold" or "pet back off" commands. Tank mercs also have an aggressive stance which means they will attack the mob when it gets close. Healer mercs have a few other stances. Efficient stance means to manage the mana better, but at the sacrifice that a damage spike might not be handled properly. Reactive stance uses more mana, but it keeps everyone healed. Balanced stance is just that.
Roles: In a group, the leader can now assign roles to people. These roles are very important to how/when the merc deals with mobs.
Puller - the merc will not follow the puller around. If there are other group members, the merc will stay with the group. If it is just you and the merc, the merc will be parked where you turned on the puller role. A merc cannot be assigned as puller.
Main Assist - the merc's main target will be the same as the main assist. The merc will not start attacking until the mob is within 50 feet of the group. The merc will try to get the mobs off other characters, but I think this is a function of AE disciplines and not by changing targets.
Main Tank - I personally think this role is broken. Even when my warrior is the main tank, I have to fight the merc for aggro. The downside is that I have to heal two toons (my warrior and merc), but at least my puller and other group members are untouched.
How do I get my merc tank to attack? First, make sure the merc is not set to passive. Second make sure your group roles are assigned. My normal group setup is warrior (MA and MT), ranger (puller), cleric, shaman, and merc tank. Tha ranger will grab the mob and bring it back to the group. The merc will stand there until the following happens:
1. The mob is within 50 feet of the group AND attacks someone in the group.
2. The mob is within 50 feet of the group AND the MA gets aggro on the mob.
I had issues with #2 when my warrior would shoot an arrow at the mob (therefore getting some aggro). The merc would meet the mob at the 50 feet radius from the group. Well, I don't like having the mob that far away. So I learn that I need to wait for the mob to get closer before I start getting aggro on anyone else other than the puller.
How many mercs can you have? Any one character can have one merc at a time. You need to dismiss that merc if you want to upgrade or change merc types. This means you will have to pay the "signing bonus" again.
Edited, Oct 30th 2008 9:39am by Pinzarn