Use WASD to move, Q and E to switch your selected tile, and the S key to place a tile. Hopefully I can do a save code system sometime, but for now the only way to save a world is to remix and click "Save Now".
It's not very original, but I wanted to have fun with everybody's favorite kitty. Enjoy! Credit to: @dragon-master for help with the scripting. @griffpatch for the Scratch Cat animation.