In the level editor mode, you can create a glitch allowing you to go through tiles very easily!
First, place a clump of solid tiles somewhere a couple tiles over the ground.
Next, place a one-way platform a half of a tile directly under the clump of solid tiles. This should be in an area where your ninja can easily jump to.
Last, press Select to begin the testing. Jump from directly under the one-way into the one-way. If you did the steps correctly, the one-way should push you into the tiles! You can jump around as much as you want until you hit a space not filled with any tile or go off the side of the map.