'Costumes'

To show the difference in the two ego's in the trailer, Dan obviously had to wear two different costumes.

The first costume, worn by the character in the woods, is made up of a stripy jumper, a Duffle coat, jeans and Converse.

 

 

This was to try make the character look as 'normal' as possible... Apparently, Duffle coats are also associated with Britishness - which may give a hint the film would be set in Britain, if it were real? Duffle coats are also quite big and protective from most elements, which implies the character is vulnerable - like Paddington Bear (who also wore a Duffle coat), so also the character could come across as quite endearing.

 

The second costume, worn by the alter ego, is a black and white suit.

 

This was intended to imply a sense of authority - smart attire assumes a position of power, and someone with knowledge. Similarly, it adds a sense of suaveness and smoothtalk with insincerity - the personality of the alter ego. Sort of supposedly quite friendly looking, but at the same time authoritative and sneaky - ready to betray his other self.