To make my game more challenging, I added a notion of kill zones - tiny disks on the ground that make the enemies vulnerable (they are not by default).

You can see the enemy turning green as the pass over the kill zone - it’s pretty hard to kill them because they need to be lured into those and it takes multiple passed to get them.

This was enough to create suspense and make it scary - you want the enemies to chase you to win, but you can’t let them get too close!