My idea is an SCP that is physically a normal person, but their anomalous properties appear when they strike up a conversation with someone. The other person will be compelled to continue the conversation and will need physical force to stop talking to the SCP. the conversation topic will be very casual and friendly, but over the course of 10-20 minutes the person will adopt the body of the SCP, and the SCP will adopt the body of the person. Basically, over the conversation they slowly swap bodies. The normal person does not notice, and when the transformation is done they will say goodbye to the SCP and walk away, forgetting the whole thing.
I also thought that maybe the SCP lives by swapping bodies, and has lived that way for centuries, if not millennia. If it gets a disease or gets old, it will swap with a younger, healthier person.