noun-modifying (irregular)
Strongly negative prenominal adjective describing someone or something as utterly contemptible or beneath consideration. Often used with nouns like やつ (guy) or 行為 (act).
He is a contemptible guy.
I cannot forgive such a despicable act.
卑劣 is a more formal na-adjective meaning 'mean' or 'cowardly', whereas 見下げ果てた is a colloquial, emotionally charged expression.
Compound of 見下げ (from 見下げる, 'to look down on') and 果てた (perfective form of 果てる, 'to end up'), literally 'ended up looking down on'. The exact historical derivation is uncertain, but the expression is conventionally associated with strong contempt.