The Assassin
The Assassin is a class that can be played in many totally different ways, as a pure Trapsin, a pure Martial Artist, a hiding Ghost, a ranged attacker or any combination. Most PvM players choose MA-Traps hybrids. Personally, I love the pure MA Sin, so here is a guide for one such build.
The Tiger Strike/Dragon Tail Martial Arts Assassin
Stat points
Strenght should be your main focus, since it both allows you to use the best equipment and adds to your claw and kick damage. If you have stat points left (which you most likely will have in the end) it's always good to put them in Str.
Dex: If you play claw/shield, you should have Dex enough to reach max blocking for your shield. If you play claw/claw as I prefer to do, you should only have dex enough for your equipment. Some of the high end claws demand quite a lot of dex though, so make sure you have points enough for the best claws.
Energy: Nothing. All Assassins except pure trappers should only have base energy since you leach up mana with items and Cobra Strike.
Vita is depending on your gear, if you have very good gear you don't need much vita actually. Whereas 200 points in Vita makes it easier to survive in Hell, it may not be necessary if you find good items, so don't put too many points in Vita early on.
Skill points
Max Tiger Strike and Dragon Tail, they are your main skills.
20 in Tiger Strike
20 in Dragon Tail
1 in Cobra Strike (to leach up mana and life)
1 in Claw Mastery
1 in Burst of Speed
1 in Weapon Block
1 in Fade (optional, depending on how much resists you have on your gear)
1 in Cloak of Shadows
1 in Shadow Master
The order in which you put your skill points doesn't matter a lot, but this is one suggestions: Start out with 1 point in Tiger Strike and 1 in Dragon Talon. You will not yet have mana enough to use it very often though. Then put 1 point in Claw Mastery and 1 in Psychic Hammer, because you want to get the prerequisites done with. At lvl 6, put 1 point in Burst of Speed, and use it all the time thereafter. Save points so you can take 1 point in both Weapon Block, Cloak of Shadow and Cobra Stike at lvl 12. If you are new to playing Assassins and using charge-up skills, practise on toggling quickly between Cobra Strike (when you need mana, you probably don't have any good mana leach items yet) and Tiger Strike, releasing them with Dragon Claw if you go dual claw, or Dragon Talon if you go claw/shield. Also practise on using Cloak of Shadow as crowd control. (Later on you can also use Mindblast for this purpose.)
When you reach lvl 24 life becomes very easy. Put 1 point in Dragon Tail and 1 in Shadow Warrior. Now, you have your main skills, plus a nice tank. I always put 1 point in Dragon Flight too, but those who want to have an absolutely perfect character sometimes use a claw switch with Dragon Flight and thus save 1 skill point! However, this build is not really tight with skill points.
1 point in Mindblast is optional, it's a very good crowd control skills that may come in handy at Hell difficulty, but it is not necessary. 1 point in Fade is also optional, it gives you good resists but since you can't use it simultaneously with Burst of Speed, you may end up not using it. My advice is to wait with Mindblast and Fade until later, and see if you need them or not.
At lvl 30, put 1 point in Shadow Master and start using it instead of the Shadow Warrior. From now on, put all your points in Tiger Strike and Dragon Tail until they are maxed. You should then be around lvl 45-48 (depending on how many of the optional skills you put points in) and it's time to start working on your elemental damage. Max Phoenix Strike, after that you can choose different paths depending on taste and what equipment you have found:
If you like elemental damage, max one of the synergy skills to Phoenix Strike. Claws of Thunder do the most damage, and in big crowds you can first release charge 3 to freeze the monsters (will do very little damage though) and then release charge 2 to dish the damage. You can also max only Blades of ice. By now you should be about lvl 78-80 or so, which means you will still have some skills points to spend on a stronger Shadow Master (11 with your gear is the perfect breakpoint), Burst of Speed (aim for 11 with gear here as well), some more in Weapon block if you are claw/claw, or something else. (Remember that both SM and BoS are prebuffable, so you can use a weapon switch with high +skills when you cast them, and then switch back to your combat weapons)
You can also max only Phoenix Strike, and instead put more points in Shadow Master, optimise your Burst of Speed, put more points in Weapon block and perhaps in Claw Mastery if you need AR.
Remember to check what lvl of BoS you need to optimise your IAS with the claws you use! IAS breakpoint tables can be found easily, I will try to post a link to one here.
Equipment
Suggestions for the average player:
Claw/s: Unless you find some special magical or rare claws that are really good, make Strenght and Malice runewords from claws with nice skills early on. Then look out for claws with +skills and large bonus to damage.
Armour: Duriel's shell, Shaftstop (give this to your merc when you find something better
), Lionheart, Smoke
Helm: Stealskull, Rockstopper
Belt:String of ears is easy to find and really good
Boots: Waterwalk, Nat's boot, rare boots with faster run/walk and resists - look out for kick damage
Gloves: Laying of hands, Magus, crafted Blood gloves, Sigons with boots
Amulet: + to MA skills and resists
Rings: Look for life leach, mana leach, dex, max damage and resists
"Godly" (best possible equipment):
Claw/s: Rare or magical claw with massive %ED and +skills, Bartuk's, Fury Runeword, Natalya's - the combinations are endless, many play with 2xBartuk or Bartuk+Jade Talon or Bartuk+Nat's. For my first pure MA sin I played with an incredible high damage rare claw and Bartuk's.
Armour: Chains of Honour, Arkaine's Valor
Helm: Vampire Gaze or Tal's mask
Belt: String of ears, Nosferatu's coil
Boots: +2 skills Shadowdancers, Upgraded Goreriders
Gloves: Dracul's grasp or rare/crafted with +2 MA skills, 20 IAS, resists and/or leach
Amulet: +3 MA and resists, Mara's
Ring 1: good Ravenfrost
Ring 2: Bul Khato's with 4 life leach or rare dual leach (mana and life leach)
If you decide to play claw/shield, of course Stormshield is the best. I however recommend you to play this build dual claw. Also, look out for skillers (grand charms with +1 to one skill tree) with +1 to MA, and perhaps one or two +1 to Shadow skills as well.
Mercenary
For this build, choose a merc you think is fun to have, without thinking of what is most efficient. I usually play with a Rouge or Iron Wolf because they are quite lousy unless you give them great equipment
and since the Shadow Master is a melee minion, and it's nice to have a ranged one too.
Gameplay
As soon as you have got Dragon Tail at lvl 24, this build is very easy to play through Normal and Nightmare. When you reach Hell difficulty, it will be significantly more difficult and you will often risk to get overwhelmed by fast monster crowds. Thus, you must start using Cloak of Shadow and perhaps also Mind blast. For difficult crowds you can cast CoS, back and recast your Shadow close to the monsters. If you play in a party, everybody will love you when you cast CoS at the feared Gloams in Hell