http://forum.a3india.com/viewtopic.php?t=1959
http://forum.a3india.com/viewtopic.php?t=438
Ok heres the deal:
Shortcut keys for merc:
Feeding pots- F7
Controlling behavior- B (don't attack) V(Attack whatever player is attacking)
and M (Defend player)
Merc window -Alt-I
Any level restriction for merc? No. Mercs just cost 500k to buy from the bar NPCs (Bellua in Quanato, Rosee in Temoz)
Can merc learn normal skills, like players(eg can HK merc heal player)? No
Can merc be traded or put in storage? No. Each of your chars will have to have their own mercs.
Can merc be pked? No
Can merc help u in pking? No (In episode 3 maps, Camarru and Bugheyr, it can and there's an option for 'assist in PK' in the merc options window)
Can merc help in PvP in arena? No. You have to unequip your merc before you can enter arena.
Which merc should I buy?
This is a tough choice to make...in general, i'd recommend the following:
Warriors-get an archer merc. They can save ur *censored* from rangers after they get to high lvl
Mages-HK merc has a robust PSP that raises your own defense. Useful esp. for ele mages.
Again-this is just my opinion..and you will have to decide which one you want. However nothing stops u from buying all 3 types of mercs; you will have to level them up separately thats all..and buy equipment for them individually.
Merc level up
You get 4 points per lvl up, as opposed to 6 points for player lvl up. You can put 2-2 in str dex for a dex build, or 3-1 for a str build. This may affect your merc's armor wearing capability.
Bear in mind your mercs attack power increases much more compared to your own. From personal experience, a lvl 90 archer merc has around 600-800 attack power...which a regular archer would get probably only after 110.
I have an alternate idea for allocating points. 3 merc lvl ups=2 player lvl ups, ie in both cases you have 12 points to allocate. So every 3 merc lvl ups, allocate your points as per normal stats. For example if you want to make your archer merc a crossbow archer, every 3 level ups when you have 12 points, divide them as 8 str, 4 dex (2 times 4,2 which is the normal allocation for xbow)
By doing this, your merc's stats will match the equipment stats and it will be easier for merc to wear equipment, although at later levels compared to the same level normal character.
Merc death
When the player dies, so does the merc. Same way, if the merc is set to attack or defend on a high lvl map..it can die off fast.
To prevent your merc from dying, set it to 'do not attack' until it has considerably leveled up. As long as the merc is on 'do not attack' monsters will ignore it. Of course, it will still die if you do...so unequip it if you're on a tough map or there are pkers running amok.
When merc dies, you have to go to Bellua/Rosee and pay 50k to revive it. After revival, merc's HP bar will be 0, so remember to again feed it pots before resuming hunt-or it will die in one shot.
Most important- Death of merc consumes your saving scroll.
Merc lvl up strategies:
Mercs get most xp and lvl up fastest from quest submission...so start questing instead of leeching!

When you submit quest, you get the same xp as you would without a merc..and the merc also gets the same amount of xp. So it's not as if the xp is divided between the 2 of u.
Those who do the jump quest will see the merc gain nearly 20 lvlups.
In the early stages, don't let your merc attack, or it will die. Press B to set it to not attack, and just continue hunting. Merc gets xp from your kills.
As long as your merc is set to not attack, creeps will ignore it. My archer merc happily runs past cynicks and they don't do anything to it

From lvl 1 to 10, one cynick=1 lvl up

Passive skills:
Mercs have various passive skills, as already mentioned in the thread links given at the top. For each lvl up, you get 1 PS point (same as for players)
You can reset your merc's stats and PS points-but it will consume your lore. That's 5 million wz to reset PS points, and 1k lore (just as with your normal character) to change stats.
Some useful info abt archer merc
Mercs have 2 types of passive skills-those that affect both player and merc, and those that affect only merc. For the archer, theres a PS called fatality. It's the bottom left skill in the skills window. This one raises the critical hit rate of both merc and player. I'm planning to max it out first.
One thing about passive points-Wait till the guides release an english patch for the merc window (it's in korean still), and more info abt skills. . Don't try putting one point in each skill cos it's a waste. Choose carefully and max your PS skills one by one. This is even more important when u get to hatrel and get PS points for your own char.
I guess that's about it for now...I will edit this post and add more info later.