Nightbane
The biggest thing to note about combining Nightbane with Ninjas & Superspies is that, while Nightbane can learn martial art styles, their innate combat abilities take over in their Morphus form. This means that A Nightbane with Tae Kwon Do would be able to use the moves and abilities from Tae Kwon Do while in Facade, but in Morphus, the innate combat abilities take over. It should also be noted that, while in Morphus, a Nightbane's Chi is doubled.

The other area of note is Martial Art Powers and Nightbane Talents.
Anti-Arcane has no effect on Chi Mastery Abilities and Chi Skills.
Atemi Again, most of these are unchanged, however they are only effective against foes not in body armor or Natural Armor. Paralysis, withering flesh, and healing Atemi are effective on and Supernatural creatures but at half damage/effectiveness.
Dim Mak does not kill Supernatural creatures, but will cause weakness, reducing their S.D.C. and Hit Points by 30% and bonuses by half; lasts until the Dim Mak touch is cured. Three successful Dim Mak attacks on a Supernatural creature will kill it, but have no additional effects.
Nightbringer, Shadow Slide, The Shroud act as invisibility with regards to Zanshin and Blind Man Kata.
See Truth, Soul Shield, Remove Face, and Piecework will not work against Chi Zoshiki. Soul Shield will work against Calm Minds.
Bloodbath will prevent a character from using any Chi Mastery Abilities or Chi Skills.
Radiate Positive Chi does 5D6 damage for Radiant Eyes, 1D6x10 damage for Radiant Flesh and Tide of Radiance completely neutralizes Darkwave if the character using Radiate Positive Chi is engulfed.
Inton Jutsu reduces the effective P.S. of Darkbonds and Air Grab by half (i.e. Darkbonds normally has a P.S. of 18 for escape purposes, Inton Jutsu reduces this to a P.S. of 9).
Shadows of Fear is half as effective against characters with Zanshin with regards to Perception penalties, the Horror Factor effect works as normal.
Characters with Zanshin do not suffer the dodge penalty of Darkwave's engulfing attack, but do not get their bonuses, they get their normal bonuses against attacks while engulfed.
Yadomejutsu and Circular Parry can parry against Dervish Dance without penalty.
Yin-Yang Kata completely neutralizes the effects of Dervish Dance...characters using these abilities both attack and defend against each other normally.
Positive Chi Spirit Burst does 5D6 damage per melee round if the character using it is engulfed by a Darkwave. Negative Chi Vortex pulls a character using Darkwave toward the Vortex. If the character using Negative Chi Vortex is actually engulfed by a Darkwave (by pulling it toward themselves), the effects are catastrophic for the Nightbane using Darkwave. The Nightbane using Darkwave gets one chance to dodge the effects of the Negative Chi Vortex by dissipating the Darkwave. If the Nightbane fails to dodge, they are destroyed; death is instantaneous.
Astral Self and Astral Projection can be detected by Chi Awareness or Zanshin and are vulnerable to Chi attacks directed at them as if they were a Chi spirit (or using Mind Walk). They. For example, any Hardened Chi, Soft Chi, Negative Chi Attacks, or One Finger Chi attacks directed against the Astral body, will do damage directly to Chi. Astral bodies can Parry or Roll with Punch against Chi attacks (without bonuses), but cannot Dodge. When an Astral body reaches zero Chi, it is dead, with no hope of any recovery. Note: Fist Gesture is the most deadly attack to Astral bodies since, if successful, it completely destroys the Astral body.

Nightlands & Chi

While the Nightlands COULD be considered a "dark alternate Earth" dimension, they're not actually that, with enough differences that a closer look at the geophysical situation of the Nightlands.
1. While there aren't a lot of areas of high positive Chi (as defined by N&S, in other words, "thick forests, jungles, and healthy grasslands") neither are there a lot of areas of high negative Chi ("caves, tombs, basements and tunnels"*...though they no doubt exist in the Nightlands).
*Above ground, the only places of negative Chi are "ugly or desolate places of darkness." This is an important note because the Nightlands are NOT a place of darkness. The Nightlands are a place of eternal twilight, with no division of night and day (which for our purposes means that the amount of Chi available won't fluctuate as it will on Earth, it will tend to be very steady, remaining within one point of it's optimal level, with the exception of the Coming of the Light, which undoubtedly temporarily increased the amount of Positive Chi).
2. The Nightlands are NOT a dimension of "unlife" therefore Positive Chi will still be the dominant surface polarity.
3. With very few areas of lush plant life and flowing water, the amount of Positive Chi will be very low.

Judging by all these factors, the amount and type of Positive Chi in the Nightlands will be very low versions of those found on Earth. Above ground will typically be found 1-3 points of Positive Chi, maybe 4-6 in cultivated areas (which brings up the interesting note of what all the Nightlord's slaves are consuming to survive...while consumption of psychic energy from Earth may explain (it's only a theory) why Nightlords and Dopplegangers are only found in the city states mirroring the Earth locations, it doesn't explain why Dopplegangers need to eat (Nightspawnbane, page 158, second paragraph)) and water sources.
Negative Chi on the other hand will be correspondingly that much higher (i.e. 1-3 points higher than the Earth equivalent, with the exception of surface areas, which are never fully dark).
I'd say that The Waste (where no random plant life exists or cultivation has occurred) will average about 2 points of Positive Chi. The Seas of Sand will have 1 point of Positive Chi. Islands will vary, depending on whether or not fresh water streams (2 without and 4 with). Sinkholes will likely have about 4 points of Positive Chi available. Rivers at least 5 points of Positive Chi, with the Western Stream likely providing 6 points of Positive Chi. The City States will be similar to modern Earth Cities, with lower amounts of Positive Chi and more occurrences of Negative Chi. The Human and Alien settlements (i.e. Kingdom of Mu-Tulan) will be closer to Earth-normal levels of Chi, with possibly a -1 to the average amount of Positive Chi.