Diablo II/Concentrate Barbarian
A barbarian based on the synergistic combination of concentrate with battle orders brings several very good things to the table. The focus is to maximize the character's survivability, usually at the cost of damage output. This starts with defense: while the difference between low and middling defense may not be much (5% misses versus 30%), with extremely high defense enemies begin to miss most of their hits (up to 95%) and the damage taken goes way down. Second is a shield with max blocking, providing an additional 75% of enemy misses. High resistances of all types lower the damage that does get through by up to 75%. With all the above and an extremely high life total, a player with this setup is a virtual tank that can survive most situations alone or in a party.
This character is good, but slow, in a solo game either soft or hardcore. With its warcries and tanking ability, it is an excellent character to play in a party alongside higher-damage-dealing characters. With its low damage dealing however, it is not a good player-vs-player character. The build is designed for version 1.10 or higher, and assumes you're playing the expansion.
 Stat points
The base stat setup is as follows:
- Strength: enough for items
- Dexterity: enough for max blocking
- Energy: base (nothing)
- Vitality: everything else
While strength does provide a bonus to damage, like with most characters it's only worth investing in it to let you equip your items. Planning ahead on this can be tricky as you may not know how many strength bonuses you'll be getting or which items you'll want. Anywhere from 120-156 base strength by level 80 can suffice here; make sure you don't underinvest and end up unable to equip yourself.
Generally strength is needed most at the start, so a lot should go into this category early on until the required amount is achieved.
Dexterity is an underappreciated stat. In addition to increasing the blocking of your shield, it provides additional attack rate, which then gets a skill bonus; the end result is that a character with a shield and max block will find it very easy to hit monsters, while one without who foregoes dexterity may have trouble hitting and be forced to invest in AR items. In any case, since this character uses a shield he needs a fair bit of dexterity.
Early in the game, aim for 2*level+15 points of dexterity as that is enough to achieve base blocking with any shield; don't be afraid to invest a few levels ahead and stick some extra points in. By level 80 or so, aim to get to max blocking with whatever "final" shield you use - with a 65% block shield (the lowest you should consider) you'll need a few extra points to get up to 75% blocking and this may take a few levels of dedicated investment so don't wait until the last minute for it.
Don't invest anything in energy. You may run into energy problems early on while using Concentrate but this will quickly go away as your damage rises and you get some minimal mana steal.
Each point of vitality provides +4 life to your character. This is further multiplied by Battle Orders, giving around 8 life per vitality point by the end. Any extra stat points (and there will be a lot) should go here. With strength mostly being invested in early on and dexterity being a steady investment, vitality points will not really start piling up until the higher levels.
 Skill points
The base skill setup is as follows:
- 20 points in Battle Orders
- 20 points in Concentrate
- 20 points in Shout
- 1-20 points in Weapon Mastery
- 1+ points in Ironskin and Bash
- 1-5 points in Natural Resistance
- 1 point in warcries Howl, Taunt, Battle Command
- 1 point in masteries Increased Stamina, Increased Speed
- 1 point in combat skills Stun, Leap, Leap Attack, Berserk
- 0-1 points in Find Potion, Find Item, and Grim Ward
The general skill progression is to get 1 point in all the crucial skills as soon as possible. Max out Battle Orders first, then Concentrate, then Shout, and Weapon Mastery last.
 Battle Orders
Though the build is called a "Concentrate Barbarian", it is really Battle Orders (BO) that's at the heart of the whole setup. You should max this out first to 20 points; it actually gives a bigger bonus to damage than investing in Concentrate does. At level 20 (ignoring +skills) it provides +92% life/mana for the whole party for nearly 4 minutes (synergized by Shout), +100 seconds Shout duration, +100 seconds Battle Command duration, and +200% Concentrate damage.
Concentrate gives the build its name and is the primary attack. Once the canonical build is completed and it receives synergies it will provide +494% damage, +250% attack, and +290% defense. The damage is low compared to most other skills and it receives no attack speed bonuses, but as a part of this build it works extremely well. The fact that it's uninterruptable is a big tactical bonus in many fights, and a huge aid to survivability. Though concentrate provides no synergies to other skills, you should max it out second after Battle Orders.
Shout is an underappreciated skill and an integral part to this build. At level 20 it provides +290% defense for the whole party for nearly 4 minutes (synergized by BO), +100 seconds BO duration, +100 seconds Battle Command duration, and +200% Berserk damage. Put 20 full points into Shout, after BO and Concentrate have both been maxed out.
 Weapon Mastery
No fourth skill provides a strong synergy for this build. Weapon Mastery is the best bet, so long as you know which weapon you will use in time to start investing for it. If you do not have a strong weapon handy, the berserker axe provides the best single-handed damage and works with a recipe for a strong crafted weapon. At level 20 a mastery will give +123% damage, +180% damage, and +21% chance of a critical strike (double damage).
If you do not know which weapon you will be using, or want to hold out to invest until you find a final weapon, extra points can be invested into Ironskin or Bash first.
 Other warcries
Howl is both a prerequisite and an important crowd-control skill. Concentrate is best when fighting a single enemy at a time; when you find yourself surrounded a single invocation of Howl can scatter the crowd for a few crucial seconds. One point is all that's needed here.
Taunt is not a prerequisite but is also a crucial crowd-control skill. This skill forces a single enemy to charge and melee attack you, and is extremely useful in a number of situations. Use it right after Howl to scatter a crowd while drawing in a single enemy for a kill; use it on a mage or archer to force them to stop their damaging ranged/special attacks and come into range to fight head-to-head; use it in a party when any monster is attacking your fellow sorceress. Again, a single point is all that's needed.
Battle Command is the third warcry that you'll definitely want. With both Shout and Battle Orders maxed out you'll receive +200 seconds duration through the synergy. A single point here with judicious use provides you and anyone else in your party with +1 skills nearly full time.
Find Potion may be worth a single point. Its biggest use is for disposal of corpses, which you might have a big problem with in a few areas. The potions it provides may also be useful on occasion.
Find Item, once you've invested a point in Find Potion, really only gives you the extra item-finding ability. Without a fair amount of skills bonuses there isn't much advantage to this, but if you're diligent with it you're sure to find a good item with it eventually.
Grim Ward, like the two above it, may also be worth a single point; in fact it may be worth investing in those two as prerequisites even if you don't think they are useful. This is a potent crowd-control tool that when used correctly can block off whole corridors or rooms for the full duration of combat, leaving large areas completely safe from monsters for your ranged-attack party members to sit or even forcing monsters to run nonstop between multiple wards. It's a more durable form of crowd control than Howl since you don't have to keep recasting it and can control the direction that monsters run, but takes a lot of practice to use well.
 Other masteries
Increased Stamina is a prerequisite, as well as being a decent skill in itself. One point here will give you the stamina to run nearly nonstop, speeding play up significantly though you still won't be able to keep up with sorceresses or paladins.
Increased Speed is a much stronger, indeed crucial, skill. Again, one point is all that's needed.
Ironskin likewise provides extra defense. The first point is the most crucial one, however putting more points here is a viable build variant. Extra points here are particularly good if you have a very high-defense set of armor, and may help you to get near to a 95% miss rate. It gives only +10% defense per level and nothing else, significantly worse than the bonuses provided by Shout or Concentrate.
Natural Resistance is yet another crucial one-pointer. Reaching max resistance is important to this build, and this passive skill lets you do it easily. If you have few +skills items, you can consider investing as many as 3-5 points here, but the benefits of the skill drop greatly at higher levels so one point is usually all that's needed.
 Other combat skills
Bash is a necessary prerequisite, and also offers +5% Concentrate damage per point. Normally it's best to just put 1 point here and then max out a weapon mastery, however if you do not know which weapon you will use you can put more here. It's also a decent place to put extra points when you are high level.
Stun and Leap are necessary prerequisite, but unfortunately have no use or synergies otherwise. These are the only two "useless" prerequisites in the build; making this one of the more skill-efficient builds possible.
Leap Attack is a one-point skill of its own, and quite important for this character. It has a much greater jump range than Leap does, and is good both for hurdling over obstacles or rivers and jumping into and out of battle. If you get surrounded and Howl fails, use Leap Attack to jump to safety. One point is all that's needed.
Berserk is another crucial side skill. As it receives synergies from both Howl and Shout, with Battle Command a single point here will get you +375% damage, nearly as much as Concentrate provides with 20 points. Of course Berserk reduces your defense to 0, exactly the opposite of what this build wants. Its crucial use however is against physical immunes: since Berserk does magic damage only, it will cut through these with no problems. It's also helpful against Oblivion Knights and other casters of Iron Maiden, as the magic damage is not reflected so that deadly curse becomes harmless. Just remember to be very careful of taking damage by using this skill, as all your defense protection is gone: the best bet is to stay behind your mercenary and let him take most of the hits.
Equipping your character is always a tricky proposition. If you have good equipment handy to trade for, you may know in advance what you are able to use and plan for that. On the other hand, if this is the first character you've beaten hell with you may have nothing saved and have to try to choose between what you find and what you can craft.
- Weapons need to be one-handed, match your weapon mastery (if any), and do high damage including a fair bit of physical damage. If in doubt, the blood recipe for crafting items combined with a berserker axe (the best one-handed base weapon) will potentially give you a very strong weapon.
- Unlike many builds, high defense is the first thing to look for in armor.
- This character must use a shield, and the shield must have high (65%+) block rate. Tailor your dexterity to max out block rate at 75%.
- Skills bonuses (+skills) are always extremely good in any item. Stats bonuses (aside from energy) are likewise good, but require a bit more preplanning if you find the item late or intend to discard it.
- As the character will be hit a lot, all forms of resistance are crucial. Aim for 75% of elemental/poison resistance, and any magic or physical resistance (which caps at 50%) will help greatly. The "cannot be frozen" protection is also a huge help to surviving.
- Manasteal and lifesteal are essential. The more lifesteal the better basically - as you will be taking damage continuously but have a large pool of hit points, the more you can steal the better able you are to brawl continuously. Very little manasteal is needed (Concentrate and other skills take little mana), but you have to have some.
- As Concentrate damage is low, anything that can increase it will speed your battles up a lot. Deadly strike and increased attack speed in particular combine well (tailoring your IAS to your weapon is an added plus). Bonus damage to demons or undead is also very helpful, as these will be some of the slowest battles. Crushing blow can speed up some of the slowest fights by a large factor.
- Prevent monster heal is essential once you get into Hell, because of high monster life regeneration and the low damage done by Concentrate. A charm of poison damage can work almost as well here.
- Anything that increases your life will get the bonus from Battle Orders, increasing its potency twofold. Life is already high to begin with but the more you have the less likely you die; this is a character that is expected to take damage in every fight.
- Avoid knockback at all costs.
The way warcries work, you can switch weapons to use them, then switch back for the next 5 minutes to fight. An effective strategy is to keep two +skills or +warcries weapons dual-wielded on your switch, for use with Shout/Battle Orders/Battle Command. Malah in Act V has a chance to sell you such weapons; the best ones are only available in Hell difficulty, have prefix "Echoing", and give +3 to warcries.
The Act 2 mercenaries have the highest survivability and provide an aura to boot. There are three viable choices to go with this build.
The Act 2 Normal/Hell "defensive" mercenary has a Defiance aura, which combines extremely well with the high-defense strategy of the build; when combined with Shout and some good ethereal armor, the merc himself may have even higher defense than the barbarian and will be a superb tank in his own right. The aura maxes out at level 20 for +260% defense. If playing hardcore this may be your best bet for staying alive.
The Act 2 Nightmare "defensive" mercenary has a Holy Freeze aura, which slows enemies down significantly. This can be quite dangerous with lightning-enchanted enemies however, so it's a mixed blessing.
The Act 2 Nightmare "offensive" mercenary has a Might aura, which maxes out at level 20 for +230% damage. With concentrate at about +500% damage this increases it to +730% so increases your physical damage by about 40%. If playing solo and softcore, this aura will provide the biggest benefit by speeding up your killing of monsters.
 Basic tips
Make sure to keep battle orders, shout, and battle command running full time, once you have them. The duration should be near 5 minutes once the warcries tree is finished, making this fairly easy to keep up with.
Your mercenary will be quite a tank in his own right. Equip him well, keep him alive, and make sure he keeps up in levels with you.
Getting the best advantage of the defense of this build means changing strategy a bit from most other characters. First of all, don't neglect the shield aspect of the build - 75% blocking means 75% less damage taken, which is particularly important against enemies that ignore your defense or when you are using berserk. Avoid running when in combat: when running your defense is reduced to zero, which will greatly increase your damage taken. Unlike most characters, this one expects to take damage in every single fight, and so to stay alive you need to minimize that damage, maximize total life, and maximize life recovery.
Practice your side skills and become proficient with them. Howl is easy to use; don't hesitate to spam it. Taunt takes only a little more effort - practice using it on far-off monsters, particularly ones with ranged attacks. Use Leap Attack often - it's better than running when surrounded by monsters. Grim Ward is the hardest skill to use, and will take practice to get the timing and location of your wards right.
 Build weaknesses
Watch out for Iron Maiden; this is one of the easiest ways to die if you aren't careful. Concentrate does almost pure physical damage and it will all be reflected back on you, potentially killing you in just one or two swings. Avoid IM by switching to Berserk when around monsters that cast it, Oblivion Knights in particular.
Monsters with ranged magic attacks are a second danger, as your defense and shield will not help against these. Protect yourself with high resistances and heavy use of Taunt to stop their attacks.
Unlike most builds, monsters with immunities are not a problem for this character. Switching to Berserk will give you comparable damage to Concentrate, and cut through them with no problem. Make sure you have a shield equipped, stay behind your mercenary, and switch back to Concentrate at the soonest opportunity.
Having said all that, the biggest weakness of this build is low damage output. This character can solo hell difficulty on hardcore and untweaked, but it will take a long time.