Follow Scratch Cat's instructions. Use the sprites in this project if you want to time travel! Also, delete the talk blocks before you backpack the sprites.
You can add sound and things to advance the time travel block. When you time travel, it switches to a random backdrop and costume but you can change the code to switch it to a certain backdrop. (Scroll too see how) First, click "see inside" and switch to the sprite called "Teleportation" Next, find the time travel block and remove the pick random block and the thing inside the pick random block. Finally, just type in the backdrop and costume number and click! You're done.