instead of saying random responses to tell the future, it responds like a normal human would (on the screen of course. Not out loud).
Yeah, we get a lot of this. Plus I think we've already got at least one, maybe two magic 8-balls on the mainlist already in different series.
In addition to this, it gives accurate answers 100% of the time.
This would be extremely difficult for the audience to believe, since typically prediction-giving "ALWAYS ACCURATE!!!" items come off as dull and predictable (pun unintended) because the conclusion is so foregone that it feels like the item is overpowered.
They can only be small stuff, like: "what will I eat today?", "will I die today?", "how will I die?", "who will I meet today?", and so forth
Most of these things are pretty easy to change though, so I personally have a hard time believing that the ball will always be accurate, especially for cases where someone's decision might depend on the ball's answer and be purposely manipulated to be different. For example, someone could just have a set of snacks on the table, they'd ask the ball which one they'll eat, and then just pick something else immediately after.
The mystery is whether the events that happen, the objects you obtain or the food that you consume are plain old objects/events or actual instances of the SCP.
This doesn't make sense since the SCP itself is an 8-ball. I think you mean "anomalies of the SCP" rather than "instances of".
I personally don't recommend writing this up. If you really want to try something along the same lines, take a look at the pages tagged with "predictive" and see how the successful ones were handled. Typically it's when the prediction aspect doesn't work 100% accurately that the story is more interesting.