### Clue: Rider went, doing a backflip, one that's out of this world (4,5)
### Answer: DEEP SPACE 
 ### Explanation: Definition: out of this world
 **Reversal of**(…, doing a backflip) [ PS(abbrev. for "postscript" from the Latin "post scriptum"/in writing, an afterthought/possibly a qualification to what's been written/a rider) + PEED(urinated/went as in "he went all over the floor") ] + ACE(one, from the playing card with one pip on it).