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
This is the Noble Phantasm of the (true) Assassin (Hassan-i Sabbah) seen in the fifth Holy Grail War, 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.

Delusional Illusion
This 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 taget really is Assassin himself.

Assassin is a single individual, but he is able to split his soul into multiple personnalities, divide his spiritual potential, and materialize the equivalent of multiple Servants. He can split into at most 80 people. He can also create a self that is unaware of that.

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

Cyber Fantasy
This is the left hand of the Assassin seen in the Heaven's Feel 3. It can turn the entire brain of the target into gunpowder to explode, blowing up the upper half of the body.

In the 4 day loop of the reenactment of the third war, Assassin grabbed the head of Bazett Fraga McRemitz with his left hand that way.

Sources: based on the Tsukihime Laboratory entry, the dictionary resource at Jonnobi and Fate/Zero #3 status page.