Getting the demon's heart
The various attacks in DHCH can be gathered via mini instances. Most of the higher rank attacks can't be farmed by lower level players, but there is a silver lining. Because you can buy DHCH skill books in the jade coin store, it is fairly easy to farm them even if you're limited to the lower level instances. Tiger Roaring Villa in the Wudang map drops the three lowest-level moves, so focusing on clearing it regularly will get the attacks you want and also give you jade tokens to buy the ones you can't farm without higher fame.
You can also buy the skill books. As I anticipated, the launch of Mt. Hua caused the book prices to drop, and now it's very common to see DHCH books in the marketplace for very reasonable rates. You might consider doing other instances that drop skill books from other styles just so you can sell them. Even though you might not want Mantis Fist books, a number of other players will and you can get jade tokens from those instance runs too.
Because mini instances are generally a pain for lower-level characters, you may want to bring a friend. It's difficult to recover energy during the boss fights when you're solo, so pairing up lets you split the boss aggro and use items for healing. Three people will let you use arrays, and the Wheel Sword weiqi formation (or other HP/MP recovery formation) makes mini instance bosses a snap. You will have to split the loot, but you'll all get jade tokens and reward chests so it's still very advantageous to do it in a group.
Who benefits from DHCH?
Demon Heart Chain Hand is largely a tai chi external style. This means it is most useful to external martial artists, while internal martial artists will have accuracy problems using it against external fighters with higher evasion. It can be used by any internal element, so all external martial artists will want it.
Even though it is an external style, it is clearly worth picking up for internal martial artists. Because it has a few unique tools, it is worth using even though its accuracy scales to dexterity. Note that I said "largely external." One attack (Devil Slay Lovers) is internal (uses spirit for accuracy), and scales to breath. This difference will affect the use of some of the style's tools.
DHCH's scalars are fairly high, so brawn (for most attacks) and breath (for Devil Slay Lovers) have a pretty significant impact on damage output. Like most martial arts, you should consider these scalars bonuses and not something you really need. There's not much point in building for them, especially for DHCH. A lot of the style's damage doesn't scale to stats.
Getting to work with the demon hands
Demon Born in Emptiness is the core of DHCH. It is a ranged knock-towards similar to the Royal Guard's chain grab, and it hits virtually instantly. It is not quite as "instant" as a lunge (there are a few things that it cannot punish, but lunges can) but it is very fast and can hit an opponent out of the recovery of many attacks on reaction.
Because an opponent cannot block while rapidly approaching, it is a fairly handy trick to use against an enemy trying to get in on you. If you hit, you generally want to follow up with Devil Breath and Demon Tramples Seven Stars to get some free damage.
The demon grab can be used to reposition enemies you need exposed. You can target an array leader or other difficult foe, pull an enemy off a horse or even pull people off of ledges. Unhorsing people is very useful in open world combat. Many people AFK and click to travel to resource nodes with auto-pathing, so you can strip your victim of his horse and kill him without fear of him running away.
Demon Born in Emptiness has a relatively short cooldown for a crowd control move, and you should base a lot of your actions around its cooldown. In the few seconds that it is down, you will want to play defensively.
Devil Slay Lovers is an unusual lunge. It has a very long cooldown and does very little. Other players tout this move as being exceptional, but it is not. It is a long cooldown lunge. It is at advantage on hit or block, which is very useful for escaping your enemy. However, you cannot link Demon Born in Emptiness afterwards, so the frame advantage is relatively small.
Demon Taoist Overrun is the style's super move. It's a buff that absorbs half the damage you take and then stores it. After the buff expires, you deal the stored damage in a wide AoE around you. If you die, the stored damage is significantly reduced (it says halved, but testing has shown the numbers to be a bit odd) but you still explode. This is a good multipurpose skill, but it is greatly hamstrung by needing rage to use. I find it most useful in duels, where it reduces the damage I take and creates a strong incentive for the enemy to run away.
Putting it together
Demon Born in Emptiness is your fight starter and your main punishment move. Whenever you land it, you'll want to combo afterwards and stick your enemy in Devil Breath. Resist the urge to combo Devil Slay Lovers afterwards. If you use your grab and end in your lunge, you have four to five seconds where you have no useful attacks. A smart opponent will feint you (since you can really only block) and crush you.
Instead, save Devil Slay Lovers for defense. If it's up, it is a valuable interrupt to use if the opponent wants to feint. If you guess wrong and are blocked, you can usually Goose away with the frame advantage on block. Do not do this against an opponent with a charged lunge super, though; you could get your slide interrupted with a perfectly-timed super attack.
Keeping your opponent in the periodic damage of Devil Breath will probably cause him to panic. A lot of people will try to get away from you; if this happens, just turn off Devil Breath and wait out your cooldowns. You actually want foes to try and escape instead of fighting back; DHCH is so-so when it comes to actual fighting, since its cooldowns are kind of long. Of course, you should try to keep a fleeing opponent in Devil Breath and keep up the charade with fake pressure. Note that your block skill will give you five seconds of enhanced movement and make you resistant to knockback, so you are hard to get away from.
If you have a charged super meter, Devil Taoist Overrun is useful as long as you have a good health pool remaining. It's sort of subtle, so you can sometimes take an enemy off-guard with it. Of course, you can also use it in group PvP situations as a suicide bomber, assuming you can build up 50 rage.
DHCH is a fantastically useful set, and learning to duel with it can catch people off guard. You'll still want to have a "real" fighting set in your school martial arts, but people are not used to seeing foes actually fight in the style and are often caught by surprise. It might only work on someone once, but if that once lets you get out of a bad situation, then it's well worth it!
Age of Wushu is a wonderous place, full of hidden secrets, incredible vistas and fearsome martial arts. Join Patrick as he journeys through China, revealing the many secrets of this ancient land. The Ming Dynasty may be a tumultuous time, but studying The Art of Wushu will give you the techniques you need to prevail.