In my game I decided to combine the enemy and pickup into one. The enemy has two parts on the body. The Front is green which destroys the ball if you're touched by it. However, if you reach the backside of the enemy, you can destroy it by touching it. 

To make this possible I separated the enemy move function from its rotation function.

This means that when the player isn't within line of sight of the enemy, it can't move and has to rotate the "head" to find you. Once it sees you it'll move towards you.

I've made two variants of this npc. The red enemy turns slowly and moves slowly.

The yellow enemy and has fast movement and turns quickly. When it loses track of the player it's forced to wait for a few seconds before it's allowed to start rotating again.

I have 2 levels. There's also a barrier below which restarts the level if you fall off the map.

It's scuffed since the camera isn't positioned properly in the first level but who cares.