Post covers of songs nobody would expect the artist to cover. Like this one. Christopher Cross must be rolling in his grave. What's that you say? Not dead? Oh dear: I do hope I left enough airholes in the... umn, never mind. Just watch the video. Clever little story and some very sexy women too.

"Ride Like the Wind" - Saxon (heavy metal band) cover Christopher Cross (Yacht/Soft rock)

i guess you can call it a crazy cover  :D

The Green Groves of Erin / The Flowers of Red Hill
by Sinta Quartet

Inspired by the brilliant versions of this from the Bothy Band

Pat Boone - In a Metal Mood: No More Mr. Nice Guy (1997)

Pat Boone covering hard rock and heavy metal is about the craziest example I can think of and he didn't just do one cover or two but an entire album's worth of hard rock and heavy metal covers!