Move with arrows or WASD. You can pass through blue platforms. If you're on one, press the down key (or "S") to fall over. Press 0 for level editor. In the level editor, keys 1, 2, 3 and 4 for selecting tiles, while 9 is for enemies and power ups, as well as the end box. Put a life over a mystery box to put it in. The piranha plants are made to be over a pipe. In a mystery box, when there is nothing, a coin appears. Press E when your mouse is over a tile to select it for the level edition. Press 0 to go back to the playing mode. When you are in the edition mode, you can pres "R" to reset the level (answer the questions to make sure it's not a mistake and to give the correct value to the width and the height of your level), or you can also press "L" to choose one of your levels, as you can save more than one. Press "Q" to activate and deactivate the auto arranging tiles. While auto arranging, press space so that it only auto arranges what you are editing and not the rest. You can crouch with the down arrow (or "S") and slide. Press "X" when you have the fire flower power up to throw fireballs. The levels are designed to test every feature of the game. It is possible to kill all enemies and to grab all of the coins. Have fun!
Thanks so much to @griffpatch for his helpful tutorials on youtube. Thanks to @Angel_Bur and @FangTest for helping me with the tutorials. More than 1000 views! Thanks so much to all of you!