This is a semi-deep guide on Nessaj. Everything in this guide is from personal experience based on Dota2 as well as ideas and perspectives from the original DotA.
The knight is a strength hero with capabilities to catch up cowards who dare to flee. You could even consider him as tank at some points thanks to his powerful ultimate, and even initiator
The knight is a powerful lategame ganker, classified as carry, although not always very reliable considering his somewhat random skills and abilities!
Personally I find him hard to play early game, but as the game progresses I tend to recap the rest of the players and usually turning the tide easy as pie.
Nessaj has a mixed set of abilities which make him slightly situational hero depending on what the opponent team setup is like.
Using the ultimate Phantasm ability could turn you into somewhat a tank for a short period of time, letting the illusions soak damage for you and your team. This would be ruined if you are unlucky to be discovered.
Early game is the toughest part for most melee heroes, even though you have considerable health pool you will take damage and perhaps even die, but don't let that stop you!
Grab two sets of tangos(6) and two healing salves. Use tango to keep yourself at 75ish % while last hitting, avoid taking as much damage as possible meanwhile.
If you happen to drop low, start retreating to a tower and use up a salve.
Boots and eventually Power Threads are your first target, prioritizing the belt due to the strength bonus is advised.
Follow up by creating the bracers for the all around stats boost, and if you have really nice gold income at this point you should consider building the drum as well, the former bracer stats are increased and you gain a perfect speed boost whenever you trigger the drum, allowing you to catch up anyone fleeing with you incredible speed.
The build is progressing, and this is the time you lay hands on the Armlet of Mordiggian; a brutal, yet cheap item. It makes farming incredibly easy, even non-activeted state, however, when you activate it you become fierce!; It temporarily adds 700 points of health to you as well as your illusions if used before Phantasm, and gives you major damage increase and haste! Use it just before ganging up on someone with Phantasm! But remember to turn it off when you start dropping in health, the drain plus the health take away will make you suffer if you happen to deactivating it during combat.
Combat and farming should by now be pie level. Roam around and gank the loners whom attempt to farm on their own! Pop phantasm around the forest corner and strike with your reality rift to finish them quickly, and don't forget your armlet, its your key item for situations like this.
With enough gold in your purse, ride off to the shop and grab yourself The helm of the Dominator. This item grants you lifestealing; increased survivability in combat and somewhat makes up for the periodic health loss from the armlet. Use the activate ability to take control of a creep and place them in the woods, this serves as a ward..sadly visible one but still useful, whenever you lose track of that single creep on the minimap; make haste and hunt down the player in that area!
After the helmet, start saving up for a Reaver, it is expensive and probably the hardest step in the entire build but this part makes life easier! A second heart for your aid. Heart of Tarrasque! This item gives plenty of strength and health bonus, as well as a side effect; a regeneration ability outside of combat; with this you can have your armlet on at all times, the heart basically gives you a total of 1000 points of permanent health boost this way. At this point of your build you should with extreme ease be able to turn over team fights to your victory!
If the mess continues and you need further items you have two choices: Either Save up for the Abyssal Blade; a guaranteed hardstun with monstrous damage output, as well as passive bash ability (the bash affects your illusions as well, but they all share the same 2 sec cooldown)...Or build further on your Helm of the Dominator!
Satanic is the ultimate item for the Chaos knight, with this blade you will stand near immortality!!! When ever you happen to drop below 50% select a target with your Reality rift and activate the blade meanwhile the knight teleports, after a strike or two, you should be healthy as a shark and unstoppable!
Two alternatives are Manta Style and Mask of Madness; From the axe you gain 2 additional illusions which benefit from your abilities and items just like the Phantasm ones, and gives you additional speed boost, as well as other general stats.
The mask gives you lifesteal like the Helmet, but it leaves you with less armor and the activation effect with more damage taken! I believe the two would word excellent together. But you have to trigger all your items and buffs before using Phantasm and Manta Style..otherwise the illusions wont benefit from the items used afterwards.
There are two viable skill builds for this character that I find useful. I have by personal and 3rd party experience found out that most of the knights skills are pretty useless and too unreliable for combat during their first 2 ranks(excluding the ultimate if you're lucky), but that is entirely situational, however, I suggest you ranking up only two at once as suggested in the skill build on top of the page.
This ability is pure chaos!
The fast traveling long range bolt stuns the target for a random period of time depending on its rank and deals random amount of damage depending on its rank.
I highly recommend to wait using this ability until mid game, or whenever you feel your mana pool can allow that, the cost of this ability is really high and taking the random numbers in mind its not worth risking early game. Instead I prefer to use it defensively to save people from being ganked on the lane or disturbing early tower pushers.
Stun Duration: 1-2/1-3/1-4/2-4
Cooldown 10 Mana 140
Ultimate ability - Phantasm-
I decided to tell you about this before the last two abilities because they benefit your ultimate as well as yourself.
Whenever you trigger the ultimate, you turn invulnerable for approximate 0.7 seconds, the knight swrabbles about and creates perhaps the most powerful illusions in the game.
They deal just as much damage as the original knight and they all benefit from your Reality rift as well as the critical strike chance! During the 0.7 secs of invulnerability you purge most debuffs away from you, making this ideal for additinal survivability.
I don't find rank one as useful, but could come in handy to gank someone on neighbour lanes, its easy to pick between two targets and check which one is the real one. Check additional tips for more info on this kinds of situations.
Remember, all your illusions benefit from your items! (excluding any forms of lifestealing sadly) Trigger your armlet before casting Phantasm to give them additional damage boost as well as additional 700 points of health; the health drain from armlet wont affect the illusions!
Number of Illusions: 1/2/3
Cooldown 140 Mana 125/200/275
Grants the ability to land critical strikes!
This ability is available for all your illusions, including rune and Manta Style editions.
This is perhaps my favorite ability in the whole wide game; it brings you and your target up and personal, allowing you a guaranteed melee hit (this does not sound very appealing I know...) But it does not only affect you, but as well as ALL your illusions (even Manta Style and Rune illusions!) Doing so will place you facing the target, and all illusions in melee range of the target, allowing them to land a strike simultaneously, at the most likely trapped target, depending on how many illusions are hugging him.
This ability could be used to gain on people, even on higher or lower planes, although there is a slight chance you might end up on different grounds anyway.
Also; if this is cast with forest in between the two players, if enough space between the trees either, might end up stuck.
As I said earlier; this ability has extremely short range during its two first ranks, making it vital to upgrade
Early game tips
Other uses for this ability are all depending on where you will end up, the ideal locations are either bringing the target to you, or move you to the target.
You can attempt forcing people staying next to your tower when they decide to flee because they are being targeted by it or your team mates. Another risky attempt is to bring targets tower hugging away from the tower, allowing you or whoever to smash the weaklings before they manage to return to the tower.
This ability is extremely rage inducing if a player keeps dying just because of it...
Early game laning is one of the most important phases for you to reach near immortality.
Lasthitting for you is vital, gather as much gold as you can for your boots, bracer(drum) and armlet.
You are not dependent on a ranged buddy on your lane, you have enough speed, especially with boots to simply run in and get the last hit before the enemies get to react too much. If you still have trouble last hitting, drag the creeps behind the tower and On the other hand; if you do have a ranged lane buddy tell him to harass the others and allowing you to farm (unless he also is a carry, make sure to split as much gold as possible) this way you will dominate the lane quickly, allowing you to push the tower with your Phantasm.
You are no good harasser until rank 4 Reality Rift, due to its range. Although strike the enemy melee player every now and then when he tries to get last hits, make him fear you and your critical strike early on!
When you have the armlet, you should be around level 11, which means you will be possessing two illusions via Phantasm, this is the time where you start shining, run out and start ganking like a mad man. Mash the enemy on lanes and start pushing whatever tower is left standing to make a fortune. Keep farming until you complete your build, sooner or later you will be powerful enough to take down anyone standing in your path!
Jungling is an alternative to farm gold when ever you lay hands on the armlet, but you may need a morbid mask to keep yourself healthy depending on your level, I suggest this only if you are missing the last 2-300 gold for something expensive, rather than risking a death and loss of gold.
Nessaj has an extremely evil and dark look, use this to your advantage!
Always have the psychological part in mind, everyone you are playing against are real people and you can combine the visual themes of your hero with the sound and noise he makes to discourage the enemy team.
During the animation of Reality Rift the horse lets off a loud and high pitched whinny, let them all know death is impending whenever the thunderhorse cries out loud!
Chaos Bolt has not very attractive visuals, and its fast moving, usually sounding like a quick fireball, I have no real tips or ideas of how to use this effect.
The critical noise coming from your swinging cudgel is fierce and loud, the illusions produce it as well, the more of it the better!
Last but definitely not least is the unique noise Phantasm makes, as well as its stunning visual effect: The horse starts whinning again, but even more fierce and now it is mixed together with rumbling rocks and thunder noises, the Nessaj and the horse look as if they are going through a blender, and within a second they split up into several illusions! Using this in front of anyone would 95% of the time scare them and make them run away, attempting to hug their towers.
If the knight does so he needs to have a chasing route, as well as an escape route in mind in case the target gets away somehow.
I would much more rather suggest one to cast the Phantasm just around the corner, before the loner or the group of players has spotted you, make them wonder what that noise was and teach them to fear it as several Chaos knights with abilities to catch up with his prey and devastating damage output charge them!
The charge above can be used to scare the team off and push them back into an ambush, leaving them few seconds of confusion and hesitation weather to attack or not!
I will eventually update this information with additional paragraphs, pictures and more userfriendly text. according to more of my own personal experience and players I personally know.
Thank you for reading.