Nanobytes' Sandbox

SCP-XXXX-1 is an entity that attaches themselves on a human, (will be called SCP-XXXX-2). SCP-XXXX-1's shape differs between every SCP-XXXX-2, most of them taking the shape of something they love (like what a child would say, an "Imaginary Friend", though it can also take form of a previous/deceased loved one). SCP-XXXX-1 can either be either an image in their minds or as a voice. (They're not physically real) SCP-XXXX-1 usually attaches themselves on humans that have feelings that they are lonely, abandoned, not loved, etc. by those around them. SCP-XXXX-1 will convince them that they are their "friend" and they will care about them more than anyone else. SCP-XXXX-2 will then develop the following stages:

Stage 1: Effects of SCP-XXXX-1 is mild, 80% of SCP-XXXX-2 have been able to resist its effects and the use of amnestics can help. (though there is a chance that they might come back again, if any amnestics is used) Its effects are not visible and SCP-XXXX-2 can still (act normally, I do not know the clinical word for this)
Stage 2: Effects of SCP-XXXX-2 is growing, only 10% of SCP-XXXX-2 have been able to resist its effects, though the use of amnestics can prevent or slow down SCP-XXXX-2 going to stage 3. SCP-XXXX-2 has difficulty socializing with others and they tend to remove themselves from conversations and prefer to be alone. Some are not even afraid to introduce SCP-XXXX-1 as their "new friend". Anyone who has known anyone being infected by SCP-XXXX-2 in this stage will have difficulty remembering them.
Stage 3: Effects of SCP-XXXX-2 is very strong, as soon as any SCP-XXXX-2 enters this stage, they can no longer be reverted back to their original state. SCP-XXXX-2 will refuse to socialize with anyone or go outside their homes and will not speak about anyone else other than SCP-XXXX-1, and believe that SCP-XXXX-1 is a real being. Anyone that has known SCP-XXXX-2 before will forget who they are.
Stage 4: SCP-XXXX-1 has taken control of SCP-XXXX-2. At this stage, SCP-XXXX-2 will completely disappear from anyone's minds and memories.

The stages of SCP-XXXX-1 can take any time from around 3 days or several years. (The length depends on how SCP-XXXX-2 acts). Amnestics can work on SCP-XXXX-2 from stages 1-3, but there will be a high chance that SCP-XXXX-1 will return (It's persistent). Anyone resistent to SCP-XXXX-1 will not be able to be infected by SCP-XXXX-1 anymore.

Summary: It's (something) that comes to lonely people claiming to be their friend. You become attached to it and you then disappear…

Story: SCP-XXXX-1 was discovered when there are several cases where there were things belonging to people's homes that they do not recognize (things like diaries, personal information, etc.) and certain residences being abandoned, but containing these objects. Similarities in the stories written in the journals about an "imaginary friend".
I could have like a log here of several SCP-XXXX-2's diaries/journals, to see their development through the stages (maybe ones with a different age, like one from a child and one from an adult)

- This is probably difficult to contain, what should be the best way to contain it?
- I don't really know what this should be other than "an entity". (Because if it's just an entity, it's going to be hard for the foundation to actually know what it is) I have a few ideas:
1. Probably like a disease or mental health problem.
2. A kind of reality bender? Maybe they can leave obvious traces somehow (I'm not quite sure)
- I've been told that this SCP is quite similar to a different SCP (SCP-126), is there a way I can move away from it so it's unique enough?