Maybe you could have the mirror have a gradual visible effect on the users physique as well as their abilities? … As for the physical effects, perhaps a slow down, reversal or even a halt to the ageing process if you sacrifice enough people? Maybe people begin to resemble their ideal selves …
I really like this idea, actually. It streamlines specifically what the SCP can do. It gives it initial effects, and then over time and with enough sacrifices it starts to really "pay off," as it were.
Backstory-wise the mirror could have been part of some exclusive club for the elite/wealthy that used its abilities for their own gain. Unfortunately for them, they happened to unwittingly kidnap a member of the Foundation. Probably a member of an SCP retrieval team who escaped and got backup after witnessing the mirror in use. The Foundation seizing it before it could be moved, but were unable to kill or capture the other members of the club. Who had already left, their ignorant staff moving the SCP out of the building for them.
That is also very intriguing. I never thought of having a cult or an exclusive club using the Mirror. For some reason, I'd seen only one person keeping it for themselves. I mean, I can definitely see there having been cults and lodges and gentleman's clubs as well as individuals of great power holding over time. I can actually see Marshall, Carter, and Dark Ltd., from what I've read on them so far, having possessed the Mirror at some point in time. Perhaps it might have been one of the few artifacts they had been unwilling to … part with, and sold only the rights to use it as one of the elite of the elite.
I like the idea of absorbing traits or skills from people. But it runs the risk of making it a power fantasy SCP. I think keeping it to creating the ideal version of a person is probably the best route to take. Maybe throw in some passive effects, like the age related stuff or becoming harder to kill. Cause it wants its users to stay alive and keep bringing it more sacrifices. Also some test logs should be added, like trying to use animal sacrifices. And attempts to damage the mirror, proving unsuccessful due to a shield it can generate? Or attacks simply phasing through it.
More good ideas and points. I don't want this to be something like a Mega Man artifact or something cliche to that effect. I think the ideal version, especially with regards to my inspiration, works better. I was toying with the idea of someone knowing or using a skill that no one else could use that reveal them and what they've done, but if the Mirror retroactively erases the victims from existence, that just contradicts itself. Your suggestion is actually much cleaner and focused.
While I'm still on the fence of a group using it, though it would make for a nice retrieval background story or information tidbit, now I'm thinking about eliminating the idea of blood sacrifice altogether. Maybe that was how it used to be done, but in reality all the users have to do is bring their victims to the Mirror and have it leech away their vitality: absorbing them until there is nothing physically left in this reality. Perhaps it's actually creepier if this process is bloodless. However, they continue to exist on the other end of the mirror as reflections.
I like your idea of one of the people using the mirror to be the one, writing the SCP page. I also like the idea of an entity inside the mirror, each person sees their ideal version of themselves when speaking to it. I imagine it can talk to multiple people and appears to each of them, as their ideal reflection. I think you could have it come off as a neutral entity that accepts the sacrifices and grants these rewards, or have it be an entity that encourages but never demands or forces its users to make sacrifices. Simply preying on good old human greed and ambition.
Perhaps the potential user sees this entity, this SCP-XXXX-1, and the reflections of all those sacrificed to the Mirror and what could make it particularly disturbing is how — perhaps the writer of the article — admits that they ignore those other reflections and how after a while, all they can see is their own. It'd be a nice psychological study in and of itself towards the very end of the piece. Maybe once they might have been scared or felt some remorse. Now, it is only just pride and an endless hunger for more power: more perfection … And all the excuses in the world will never negate the truth: which is that they chose to listen to the entity that embodied their perfect self. They chose to ignore the victims and their suffering. They decided that they were more important.
Maybe throw in some passive effects, like the age related stuff or becoming harder to kill. Cause it wants its users to stay alive and keep bringing it more sacrifices. Also some test logs should be added, like trying to use animal sacrifices. And attempts to damage the mirror, proving unsuccessful due to a shield it can generate? Or attacks simply phasing through it.
I like how it preserves its users so that it can continue to gain more sacrifices. And the animal sacrifices are an interesting test. I'm actually not sure what would happen: if they would just not work, or if there was some adverse effect, or some small benefits. As for its protection, I can see the Mirror actually being very solid. For all it is made of obsidian, perhaps it was forged with a lost art that makes it as strong as the hardest diamond. It only gets porous through sacrifices.
(Now I am wondering what happens if you put a bomb in one of the victims that goes through. Wow, that is dark.)