A Mixed metaphor is a phrase in which two or more figures of speech are contradictory, ludicrous, or impossible when visualized as if they were literal. In some cases, the tropes don't meet this definition but still clash awkwardly or create a string of eye-rolling clichés. I've dubbed this latter phenomenon a mashed metaphor.
"It's all Low-Hanging Fruit on Steroids: Many More Mixed and Mashed Metaphors,"
Word Ways: Vol. 50
, Article 14.
Available at: http://digitalcommons.butler.edu/wordways/vol50/iss1/14