Sidescroller Enemy Spawning

Here’s what would like:

  • Enemies spawn at specific locations (or just random locations as long as they’re generally evenly spaced…)

  • Enemies only spawn outside the screen.

  • The enemies that spawn are random (from an array of possible enemies for each level)

  • Enemies should chase you, but once they are far enough outside of the screen they should be destroyed.

I tried having the enemies spawn every so often and set the location to be within a certain range ahead of my character. Problem was, if I stop running enemies keep spawning and creating a cluster of enemies in front of me. I want the player to be able to put down the controller and not have to worry about coming back to a giant mob.
We also wanted the player to be able to run back and forth (left and right) through the level and keep killing enemies indefinitely.

Anyone have any ideas of how to handle this? My brain can’t figure this one out…

Um… Bump…?