SCP Foundation

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.

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?

Why is anyone allowed into the containment chamber at all?

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.

Seems a little reminiscent of the typical "eternal youth via life/energy/soul draining" premise. Lots of examples of this in popular media, like Selene the "psychic vampire" from the Marvel Universe. More examples and similar versions in this listing: https://tvtropes.org/pmwiki/pmwiki.php/Main/VampiricDraining

Personally, I'm not too sure about this. It seems like a pretty generic power/motivation so far as humanoids go, and there have definitely been similar attempts done, vampiric or not.

Humanoids are actually among the most difficult types of articles to write successfully; if you're really set on writing one, then first take a look at the humanoid writing guide if you haven't yet.