In college I played Nethack. Then I moved to Moria. Now I stick to playing Angband.
I got the player fighting monsters now in my 7DRL entry Room Rogue. Players hit monsters. The monster hit back. It is a battle to the death. Right now the battle system is very simplified. If you are in range of a monster, you can always hit it. And you always do max damage. Same thing goes for the monsters. If they can reach you, they do hit you with maximum damage every time.
I stacked the odds in favor of the player. They always auto heal. And they do more damage than monsters. The monster also have a very dumbed down navigation. They get jammed up and cannot approach the player in all kinds of scenarios. I was able to move through this unbalanced game and get halfway down the dungeon before getting bumped off.
I need to employ the RNG and check a random number every time somebody tries to attack. And if the number shows there was a hit, I need to compute a random amount of damage. Otherwise things will be too predictable. Now sure if I am going to allow the monsters to regenerate health like the player or not. Maybe they can do it at a much slower rate.