Who tucked me in last night?

Who was that? That was an Amalgamate. This Amalgamate is unnamed and appears in the pacifist router. By the looks of it, it's sole purpose is to tuck you in.

An unnamed Amalgamate can tuck the protagonist into bed, should they decide to lay down in it and remain still for long enough. The Amalgamate then pats the protagonist on the head and disappears

While this Amalgamate may not have a name within the game itself, the sprite of the character within the game's data files is named watchingman