This guide will focus on lightning sentry and death sentry for traps, and using a shield. There are many advantages of using a claw/claw setup instead of a shield, so that option is open as well.
Stat points
With this assasin you never have enough stat points. You have three stats that is important for you, so you should be a little bit carefull when deciding.
Strength: Strength contributes most to your damage. You should try to have a high strength, but get as much as possible from items. Its no point in doing much damage if you can't take a punch.
Dexterity: Enough to have max block with your shield. See my blizzard soceress guide for details about this. (If you play claw/claw you should only have enough to wear equipment)
Vitality: Here you should place a lot of points. You need to survive.
Energy: No points should be wasted here under any circumstances.
Skill points
15 - 20 in Dragon Talon.
Dragon talon will be your main attack skill, and also the skill you spend points in first. For every 6 levels of Dragon Talon you get an extra kick. This is the only thing that really matters witch mean that with the bonus from your equipment your total score should be 18, 24, 30 etc. So if you only have +2 from equipment there is no sense in putting more than 16 points in this. Most likely you will get far more than +2 though, so this skill will probably be between 18 and 20.
20 in Lightning Sentry
20 in Death Sentry
3 in prerequisites for those
This will be your two traps. Death sentry works as a synergy to lightning sentry and vice versa. If you have points to spare you can put them in another of the synergies to lightning sentry, for example Charged Bolt Sentry.
1 - a few in Burst of speed
0 - a few in fade
Both of these are excellent skills. Unfortunatly you can only have one active at a time, so you should decide wich one to focus on and then customize your equipment after that and place no extra points on the other. Fade gives resists and a little bit physical resistance, while Burst of speed gives you increased attack speed and faster run/walk. You should not put to many points in Burst of speed even if you decide to focus on that one because the gains on higher levels are very small.
0 - 1 in Mindblast
0 - 1 in Cloak of shadow
0 - 1 in Dragon flight
These skills are good utility skills. You can use them or you can ignore them. They are good at only one skill point. Both Cloak of shadow and Mindblast gives you a bit of crowd control. Dragon flight is overrated in my opinion. The casting delay is so long that it is not really usefull for getting out of hot spots, its mostly good for making transports more convinient.
10 - 20 in Shadow master
The shadow master is an excellent companion and you should definetly use it. The more points you can put here the better. The development is quite linear so there isn't any special skill level to aim for.
The rest of your skill points you can use as you se fit. The best option is probably to put the rest in lightning sentry synergies. Another option available to those who have choosen to focus on fade is to max it. It will not raise you resist very much, but it will give you a 20% physical resistance. Remember that physical resistance is capped at 50% though, so don't max it if you plan to use equipment witch will bring your total higher than 50.
Attack speed
Dragon talon works in the following way. Each time you make an attack the assasin kicks multiple times towards a single target. The first kick is quite slow, but follow up kicks are quick. The lowest possible attack time for the following kicks are 3 frames per attack(Fpa) and this is what you should have. The attack speed without any increased attack speed(IAS) and with a weapon speed of 0 and no Burst of speed is 6 frames per attack. Your attack speed depends on your effective increased attack speed(EIAS) wich is calculated in the following way:
EIAS = ((120*IAS)/(120+IAS)) + Burst of speed bonus – Weapon speed
After calculating your EIAS you read the following table:
EIAS Fpa
-30 6
-19 5
0 4
34[indent]3[/indent]
For example, if you use a greater claw and don't use burst of speed you will need 5 IAS to reach 3 Fpa.
Crushing blow
The quick attacks granted by dragon talon should be used to apply different bonus modifiers, and one of the best of these are crushing blow. If you have equipment that gives you crushing blow there is a chance on every attack that the monster will loose 1/4 of its hitpoints. It is essential that your equipment should provide as much crushing blow as possible.
Not all bonus modifiers works on your kicks, but here are some that does:
Elemental Damage
Magical Damage
Chance to cast X on striking
Open Wounds
Prevent Monster Heal
Ignore Target Defense
Hit Blinds Target
Hit Causes Monster to Flee
Hit Freezes target
Hit Slows Target
As you can see a few of these can be very good. Elemental damage might not look much but remember how fast your attack is. If you account for this it might provide a substantial damage bonus.
On the other hand, Chance to cast X on attack and Enhanced damage on your weapon and added physical damage on your other equipment does not carry on to your kicks.
Boots
You can't make do with only crushing blow though, you should try to do a bit of ordinary damage as well. The damage of your kicks depends very much on your boots. The heavier the boots the more damage you do. Myrmidon Greaves is the boots that does most damage, so you should always try to use these in the end. You can uppgrade War Boots and Greaves to Myrmidon Greaves if you have a pair with good modifiers.
Mercenary
You are very free in your choice of mercenary. There are no real position that needs to be filled as you will be a very all-around character, and you have an excellent shadow master as well. This means you can choose whatever you feel like. Even those horrible mages from act 3 are viable choices.
Gameplay
As you soon will notice you won't have any problems whatsoever with bosses. Your quick attack and crushing blow will have them dead in no time. Your biggest concern is crowds of quick melee monsters, and monster who are both physhical and lightning immune. When it comes to most crowds you should use death sentry and then attack them physically. Hopefully you will soon get a chain reaction where one monster explodes another, but with heavy hitting melee monsters, like Lister's pack, this might not be an option. In that case you should instead take your time and break up the pack in manageable pieces. When it comes to monster that are both physical and lightning immune you can use death sentry witch does 50% fire damage, and you can have a weapon switch with some elemental damage. alternatively you can use an act 3 merc who does fire or cold damage, but that will be a pain.