Mixed idioms are fun and little bit goofy. It’s when two well known phrases with similar meanings are mixed up—by accident or deliberately.
A few examples:
“Until the cows freeze over.”
(Until the cows come home; until hell freezes over)
“A walk in the cake.”
(A walk in the park; a piece of cake)
“Let’s put the elephant on the table.”
(The elephant in the room; lay your cards on the table)