In case you weren't aware, Super Smash Bros. for Wii U features dialog similar to Snake's codec conversations in Brawl. They're called Palutena's Guidance, and they're activated by Pit's down taunt on Palutena's Temple. Pit, Palutena, and others will directly comment on the characters Pit is currently facing, to humorous effect. However, there is one piece of dialog that doesn't seem to be associated with any one character…
Hidden in the sound data is a piece of Palutena's Guidance that isn't heard in normal play. You can listen to it for yourself here:
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.
It's speculated that this is generic dialog heard in a match with a DLC character. Smash director Masahiro Sakurai has previously said that Mewtwo is the only DLC fighter that the team is planning. The inclusion of this dialog, however, suggests that they further DLC characters is more than a mild possibility.
I guess we'll find out in due time!
