Traumobra's denotation as the "It Pokemon" is a reference to the novel and movie "It", in which an omniscient being commonly takes the form of a clown.
Traumobra is based off of clowns and the related childhood fear of them. It references the "killer clown" movement that was popular on the Internet. It could also be a reference to snake clowns from the Lego Batman movie. The shiny form is based on the Joker from the Batman Series.
Traumobra is a combination of "trauma" and "cobra", as a reference to the trauma some kids may experience when seeing a clown. It may also incorporate the word "Coulrophobia" meaning a fear of clowns which some anon probably thought sounded like "cobra"