This game badly needs an update to improve stability. I am unable to defeat Ripper Roo because he will randomly stop dropping boxes and sit there. Nothing I do has an effect on him, and I have been forced to randomly quit the level at least 20 times only for the same result.
If you're referring to the glitch where Ripper Roo gets hit, gets smokey explosion all over him and just sits there. The glitch was put there on purpose as a way of making the game more difficult, and because it was in the original game's code in another form, to undo this glitch, simply exit and restart the level.
On a side note, are you refferring to Crash 1 or Crash 2, because Ripper Roo is defeated with a spin attack while stunned by the TNT or Nitro Crates in Crash 2. In Crash 1: Ripper Roo is defeated by jumping on a TNT crate next to him. But avoid blowing him up while he's stunned or else Ripper Roo will turn invincible.