Pit: Who is that?
Palutena: I have no data on this fighter. I can't believe it.
Viridi: It must be an intruder from another dimension.
Pit: Whoever it is, the goal remains the same. To fight and win.
Your guess is as good as mine on who this could be for. Granted, it could be a generic conversation for any future DLC characters, which would imply more DLC characters beyond Mewtwo (who would have his own Palutena's Guidance conversation if he really was the only DLC character). It could also be a placeholder during development.
Source: Vocaroo