Board Thread:Wiki Discussion/@comment-28912103-20170319045254/@comment-27701762-20170319065629

Post hoc, ergo propter hoc.

It doesn't really mean anything that Napstablook only starts appearing once you encounter the first dummy, since it is not possible to not encounter the dummy, nor Napstablook.

In contrast, upon encountering the dummy, you can do any number of things to it without impacting the way Napstablook interacts with you: if you talk to the dummy, Napstablook never mentions that Frisk said mean things; if you attack it, Napstablook never mentions being attacked; if you bore it, Napstablook never mentions being bored out of his old body. No matter what, Napstablook reacts as though he never encountered you before.

In addition, Napstablook is dismayed that one of his cousins left to inhabit a dummy, and is similarly worried that Mettaton will leave him all alone to take care of the snail ranch. Nor does Napstablook appear to want to abandon his duties at the ranch, which he would need to do if he was inhabiting the dummy in the Ruins.

Given the above, the dummy is in all likelihood a fourth ghost, definitely a cousin to the Mad Dummy, and perhaps a cousin to Napstablook.