I tried to familiarize myself with the Unreal Engine 4 and its blueprints by scripting my own AI and combat mechanics. I used the First Person template (which comes with the playable character and the gun) and added an enemy character with its own AI and decision system. Even though I was going for a fun shooting level without any health or death, it eventually turned out to be a pretty creepy enemy who manages to find you eventually and shoot at you, somewhat like in the Terminator movies.
I made a behaviour tree for the AI (shown below) which consists of 2 phases: "Shoot" and "Search". The enemy shoots at you at least once in 3 seconds if he can see you, and if he loses Line of Sight then he moves towards the position where he saw you last, and looks for you again. The enemy is a navmesh agent so he can move anywhere in the field freely, and I did the level design in such a way that it is easy to hide but the enemy seeks you out eventually, and consistently