I'm gonna enjoy this. I probably made a few of these abilities needlessly more complicated than they would be in the manga. I have come up with abilities only for 6 Zodiacs, plus one for Sacchou, but it has nothing to do with his animal, so I left it out. Here I listed them from in what I imagine to be an abstract order of strength of the users, from strongest to weakest (counting physical prowess, strategy, combat and Nen abilities; but then again, it is only speculation):
SAIYU (Manipulation)
Name: Three Monkeys
Nen Type: Emission, Manipulation
Description: Saiyu creates three monkeys out of his aura. If their attacks are successful, they deprive the opponent of one of his faculties: Mizaru of his sight, Kikazaru of his hearing and Iwazaru of his speech. Saiyu can increase their chances to hit by timing his own attacks with theirs or by hiding them with In. The monkey can either move automatically or follow Saiyu’s direct mental commands: when they fight together, it is usually the latter. The auto-mode will slightly lower their physical abilities (speed, strength).
The ability also has a secondary use. Instead of targeting the opponent, Saiyu can order the monkeys to steal his own senses. Depriving himself of speech barely affects his aura at all, while the loss of sight causes it to receive the most prominent boost. If he loses more than one faculty, the increase in aura output is given by the multiplication of the benefits granted by every single sensorial loss, rather than by their addition.
Limitations: Since Nen puppets are generally weaker than the ability user, Saiyu utilizes several limitations to make the monkeys faster.
Saiyu can only generate one monkey of each type.
The monkeys can attack only one target. It is impossible to change target once one of the monkey’s attack is successful.
If the opponent touches a monkey (or vice-versa) after it has stolen one of his faculties, the opponent will reacquire the corresponding faculty.
Same if a mankey is damaged enough or Saiyu (or someone else through a Nen-cancelling ability) makes it disappear.
If a monkey ventures too far away from Saiyu, it disappears. Each of them has different limits: Iwazaru can go only as far as Saiyu’s voice can reach, Kikazaru where Saiyu can hear it, and Mizaru where he can see it. Obstacles are not counted.
CHEADLE (Enhancement or Conjuration)
Name:
Nen Type: Emission (if she is an Enhancer) / Conjuration (if she is a Conjurer), Manipulation
Description: Cheadle creates a huge St. Bernard out (of her aura. The dog is big enough to be ridden by multiple people at once, and boasts fearsome strength, speed and stamina. Its primary ability, however, is its capacity to absorb microorganisms through its tongue (for example by licking a sick person) and store them in the canister secured to its throat. A meter on the canister will indicate when it is completely full. The dog can also inject said microorganisms into a target by biting him/her. Although the St. Bernard is the species Cheadle elects, she can also create normal-sized dogs of many different species.
Limitations: The dog can be dispelled at any time, but a canister can disappear only when it is empty. A canister can hold only a single type of cell/microorganism, with each dog being equipped with only a single canister.
GINTA (Enhancement)
Name: Meteoram
Nen Type: Enhancement
Description: Ginta starts the ability by focusing a huge amount of aura in his head using Ko. The longer he remains immobile, the more aura he can muster. Then, exploiting his impressive speed, he urls himself at the opponent, gaining momentum as he runs, before finally headbutting them with tremendous power.
Ginta can also use a much quicker variation of this ability, which is more suitable for close-quarters combat: he smply uses Ko with barely any preparation and attacks with a headbutt. Even though this version is much weaker than the original ability, it can rival Uvogin's Big Bang Punch in terms of sheer power.
Limitations: In description.
KANZAI (Emission)
Name: Tiger's Eye
Nen Type: Emission
Description: Kanzai creates a small sphere of aura in his hand and throws it at the target. Before throwing it, he can choose its size. While the power and speed of each bullet is the same, bigger bullets will inflict more damage thanks to their superior size (they will also consume more aura), while smaller bullets will be able to cover more distance.
Limitations: None, strictly speaking. However, much like Franklin, Kanzai strengthens his Nen in this attack by:
altering the shape of the orb to make it resemble a tiger's muzzle.
throwing it pitcher-like. The more fluid his movement, the stronger, faster and more precise the attack.
GERU (Conjuration)
Name: ...
Nen Type: Conjuration
Description: By turning her arm into a snake and having it “bite” the opponent, Gell can inject them with her own blood transformed into a poison of her choice: some merely paralyze the target, others can kill him. All poisons are very powerful and quick to take effect. By biting the target again, Geru can reabsorb her blood and thus remove the poison, making it an effective interrogation technique, although she cannot revert the effects it has had up to that point. Using the same procedure, she can transfer a poison from a target, to herself, and then to another target, provided she has a good understanding of the poison in question.
Limitations: In order to make her snake arm(s) even faster, Geru has come up with two limitations: before biting an opponent to inject a toxin made out of her own aura, Geru's snake arm must first make "eye contact" with the opponent from a very short distance; also, since the poison is actually Gell’s blood, she can use this ability only on a limited amount of targets before the blood loss becomes an impairment.
PIYON (Transmutation or Emission)
Name: ...
Nen Type: Transmutation, Emission
Description: Piyon creates platforms out of her aura to change direction, accelerate, retreat to safety and in general move freely even in midair. The platforms can also be used as shields or to entrap a target. Piyon can also manifest them away from herself, but their durability drops in this case. She is adept at creating them while using In, leading the enemy to believe she is floating in midair. When combined with her immense speed and agility, as well as her kick-based martial art, make Piyon an unpredictable fighter and a real threat in close quarters combat. Due to her mobility far surpassing her opponent’s, she can devote all her strength to attacking, using high-damaging techniques such as Ryu and Ko without fear of being hit. If she manages to lift her enemy from the ground, it’s Piyon’s victory, as she is the only one who can move without foothold.
Limitations: None.
OR
Name: ...
Nen Type: Emission
Description: Piyon creates two platforms, one black and one white. By touching the white platform, she will be instantaneously teleported to the black one. The platforms do not disappear until Piyon wills them to, meaning they can be used multiple times. The consumption of aura on Piyon’s part depends on the size of the platform (which must be at least as big as the object for the ability to work) and the amount of time it has been into existence. Since Piyon needs to remember which white platform leads to which black one, each pair of platforms bears a different number, although this makes her movements more predictable for the opponent. A downside to this ability is that the effect applies to whoever touches the platforms once they are active, including Piyon’s enemies.
Limitations:
Piyon must mark the locations on which she wants both platforms to appear, with her right hand for the white one, with the left for the black one. Then, to manifest the platforms, she must step on the white mark, which will immediately teleport her to the black platform.
This also means the platforms can only be created on immobile ground (not a river).
She must always create a white platform and a black platform at the same time.
Multiple platforms can be created at once, but a white platform will always lead to the same black platform.
Stepping onto a black platform without having been teleported there will cause both the black and the white platform to disappear.