Example 2 of my screenshots for YSQ.

Here you can see part of a level. Section 1 is an obstacle - the dog walks on its own back and forth path. It's invulnerable to enemies, but otherwise behaves like a green koopa - walking off edges. Using On/Off Switches and P-blocks, he must be guided back through a level.
Picture 2 is the nearest P-block.
Picture 3 is the /second/ nearest P-block.
Picture 4 is the obstacle that the dog needs the P-block to cross.