Zabaniya

Zabaniya is the name of the Noble Phantasms of all the 19 Assassins. The same name was used for the mystery each of them had - they each had their own to surpass the 18 others, but they were all named the same.

Delusional Heartbeat
Delusional Heartbeat (妄想心音) is the Noble Phantasm of the (true) Assassin (Hassan-i Sabbah) seen in the Heaven's Feel 5. It is the arm of the evil spirit Shayṭān, the cursing hand of the Middle East magecraft specialized in curses; the right hand of Hassan.

It creates a mirror image of the heart of the assassination target with an ether clump, a dual existence that resonates with the original one. By crushing the fake heart, he can crush the real one with this curse without laying a finger on it. As he is really crushing a fake heart, any physical defense is meaningless. To resist the curse, it is not endurance that matters, but the magical power, to prevent him from creating the dual existence at all.

Incidentally, it is also possible to make the fake heart exchange places with real one, but for that he must first touch the opponent's chest. It has no effect on other evil spirits or those whose hearts are already corrupted by another curse, such as is the case with Kotomine Kirei and Dark Sakura 

Delusional Illusion
Delusional Illusion (妄想幻像) is the Noble Phantasm of the Assassin seen in the fourth Grail War, Heaven's Feel 4. It is ranked as an anti-unit Noble Phantasm, but the target really is Assassin himself.

Assassin is a single individual, but he is able to split his soul into multiple personalities, divide his spiritual potential, and materialize the equivalent of multiple Servants. He can split into at most 80 people. There is a chance for him to lose his sense of self by doing so.

The stats are also divided, so this does not really equal a small army. 

Cyber Fantasy
Cyber Fantasy (空想電脳) is the ability of the Assassin summoned during the Third Holy Grail War. Upon contact between an enemy's head and one of Assassin's hands, it turns the target's brain into gunpowder, causing it to explode and destroy the upper half of their body. Assassin was a midget of a height no taller than up to an adult's knees, so he was able to blend in with his doll user Master's dolls to obstruct his presence. He uses this tactic to surprise Bazett Fraga McRemitz during Fate/hollow ataraxia to strike her with poisonous needles to paralyze her legs, and manages to grab her head with his left hand due to being one of the fastest Servants and one of the hardest to properly target due to his size.

The Delusional Fantasy of no Laws/The Lawless Delusional Fantasy
Is the Noble Phantasm of another Assassin that is belived to be The Ultimate Assassin. It works in the concept of a reality marble and allows Assassin to excess all the

abilities of the other Assassins (with the exception of Assassin). Assassin is also able to trap his enemies and disable them from using their powers, as well as steal their life

force and energy and use it as his own. Assassin activates it by using a mass of his own energy and some amount of his life force (he continues to use his own life force and

energy to keep it stable). But the chances of Assassin losing his mind is at a high risk and during this state he may lose his own life force and energy before he can steal his

enemy's/enemies' is high as it requires a lot of power and causes great strain to Assassin.