I prefer theme 2 but this is
From the description of ‘Darkrai’s Theme’ (1)
"A nice, creepy song with a catchy beat and tune to give you the chill of Darkrai’s dark aura." by YouTube user dragonflare1000
Info on Darkrai from Bulbapedia entry
"Darkrai is known to "inhabit" dreams and causes the target to have unending nightmares …However, the "unleashing of nightmares" is actually a defense mechanism, instead of an intentionally malicious act. It can become a shadow and escape danger or contact of humans. It is also capable of little human speech."
(As mentioned in Chris Petit’s ‘Content’ )