A student in my games class is implementing a basic platform game following the same basic guidelines that are at the core of the official C3 tutorial for this type of game. (The only difference is that we're using sprites to create the environment rather than using tile maps for the environment.)
Enemy movement is handled by simulating platform controls and using collision with an invisible barrier to reverse the direction.
This is mostly working but the enemy is falling through the island when it reverses direction. Everything is fine when we make the terrain 'solid' instead of 'jump-through,' but we want to have jump through functionality.
The link to her C3P is: