Psychedelic-420, also Psy-420 or just P-420, is a rather unpopular, not very well-known, fan-made alternate of Shizuo Heiwajima. Supposedly, he was a failed prototype of Psychedelic Dreamer 02, more commonly known as Delic. He is mostly shown as a type of anti-virus program, living in a digital world with Virus 138.
P-420 has an arrogant and violent personality. Some fans think that his violent tendencies are cause by some degree of clinical insanity, making him even more dangerous than Shizuo Heiwajima. He can be a rather dark and twisted character.
Psychedelic-420 seems to represent the violent side of Shizuo's personality.
On rare occasions, he is portrayed as emotionless.
P-420's outfit is similar to Shizuo's with a few distinct differences. He wears a white dress shirt underneath a black vest which, on rare occasions, has green highlights. Unlike Shizuo, who wears a black bowtie, P-240 wears a green tie which is usually loosened. He also wears a pair of green-tinted shades and a pair of short, black gloves. He wears green headphones that are also either black, white, or both. In fanart, he's often smirking while holding one or two guns, giving him a sort of badass look.
Fans tend to always ship him and his counterpart, Virus 138. Together, they have a love-hate relationship similar to Izaya's and Shizuo's.
(See more on Virus 138's page)