adocenar

A literary verb meaning to make something or someone mediocre, ordinary, or run-of-the-mill — from docena (dozen), as in lumping something in with an undistinguished crowd. Mostly seen in critical or literary writing, not daily speech.

• La crítica dijo que el escritor se había adocenado con los años. — The critic said the writer had grown mediocre over the years.
• No quiere adocenarse repitiendo las mismas fórmulas. — He doesn't want to become run-of-the-mill by repeating the same formulas.
• El estilo adocenado de la novela decepcionó a los lectores. — The novel's uninspired style disappointed readers.

There's no everyday common mistake here — adocenar belongs to literary/critical registers, not something a general learner needs for daily conversation.