Reverse GIF
Play a GIF backwards, or make a boomerang that goes forwards and then backwards in a seamless loop.
Direction
A boomerang plays the frames forwards, then backwards, so the loop has no jump.
About reversing
Reversing keeps every frame and its timing, only in the opposite order. At the default quality of 100 the frames are stored exactly as they were. A boomerang is about twice as long, so the file grows too; Compress can bring it back down.