just some of a random test (:P) [lel lol :skull:]
----what i did---- tbh all i did is make using basic movement animations, then created a new costume for the trail (check it inside) then created a new clone everytime you press the arrow keys and on the 'when i start as clone' block you just add the blocks 'set size to (75)', set costume to (the new costume you made for trail), wait for (0.75 seconds) and then finally delete this clone. (i was to lazy to type the thing where you hit the edge you go to the other edge or whatever sorry just check it inside) i hope this helps :D (probably not but dont need to credit if u use :D)