mixed metaphor 
noun
A combination of two or more incompatible metaphors (e.g. this tower of strength will forge ahead).After a couple of weeks out of the game I came out of the blocks like a prize fighter wielding a mixed metaphor simile cliche and battered everyone in my path....
- Multiple mixed metaphors proliferate until there is no ground whatsoever under the reader, syntactical functions become precarious, sound and vision seem to rule over anything else the poem might bear.
- Even so, that has got to be one of the worst mixed metaphors ever.