A save warp is where you set up a save point in one room and die in another, sending you back to that original save point. This can be abused in the Backwards category of Hooked (not Any% or Hookless as far as we know) and can save around 20 seconds. However, the setup for this can take some time and can be inconsistent.

To set up this trick, you activate a save point at the start of the "Double shroom" stage and make your way to the end, without touching any floor. Mushrooms and leaf blocks often don't act as save points but they sometimes can. You can tell if you have activated a save point on either of these blocks if you hear the touching ground sound effect while on one of them.

The setup is shown in the video (linked above) which walks you through it and should help you to perform a save warp.

Note: Save warps only work in versions 1.1+ and not 1.0.