Alright, time for my second Blog Post.
This time we're looking at the phantasm belonging to True Assassin, Zabaniya: Delusional Heartbeat.
This Phantasm makes use of the severed arm of the demon, Shayṭān, that has been attached in place of True Assassin's right arm and is used to inflict a fatal curse upon his enemies, forging a false heart in his palm before crushing it and mirroring the damage onto his opponent. As seen in the accompanying image, as well as being grafted to his right arm, the position of the thumb shows it to be the demon's right arm.
Meanwhile, with the appearance of Fate/Strange Fake, we're introduced to the Beautiful Assassin, a candidate for the position of Hassan who managed to learn all of the other Zabaniya techniques with the exception of Delusional Illusion, as that belonged to the guy who would get the job in her place. Her version of Delusional Heartbeat is a little different in execution, but more importantly to this topic, it is not replacing either of her existing arms, instead being grafted to her back. The image there displays her use of the technique against her master and while at an incredibly odd angle, it is possible to inspect the image and determine that she does, in fact, possess the left arm of Shayṭān, as opposed to True Assassin's right. So rather than harvesting the existing arm from the past leader, the candidate seemingly went out and got one for herself.
So in conclusion, the Assassin order went out and made poor Shayṭān, quite, quite 'armless indeed.