Nobody knows how he got here, but he's just so nice to keep around. Quiet, but not too quiet, and able to carry a conversation with ease.
I mean sure, I'm always a little more tired than usual when I leave his containment chamber, and every day he looks a little bit younger, but he's just such a nice guy, you know?
Dan is an anomalous entity that rapidly drains the energy out of anyone in contact with it for over fifteen minutes, using the energy to maintain its appearance of a healthy adult man. Anyone in contact with Dan will perceive it as extremely friendly, and like it almost immediately.
So, is this a good concept? I'm worried that there's already an SCP that's used this premise before.