delusional; chimerical
Describes ideas, beliefs, or perceptions that are fanciful, unrealistic, or detached from reality. Often used in psychological or critical contexts.
His plan is delusional; I don't think it will come true.
He is possessed by chimerical ideas.
Derived from 妄想 (delusion) + 的 (-like, -ish), forming an adjectival noun meaning 'delusional' or 'chimerical'.