DoomRL tips:

The Wall is a bit tricky but there's an easy way to beat it. Upon entering, keep going forward and you'll be faced with a destructible wall. The idea is that you blow a hole through it with a rocket launcher. But there are about a dozen hell knights/barons behind the wall. The technique to beat it easily is to dig a hole through either the uppermost part of the wall or the bottommost part of the wall then you camp in the corner of the wall and cornershoot those hell knights/barons with high knockback weapons (shotguns) as they approach you, if done right you should practically be untouchable. Your goal is to make the gap in the wall as narrow as possible so the barons won't be able to get to an angle where they can shoot you while you shoot them from the corner.

The missile launcher is like the rocket launcher but you can fire four rockets before reloading and it has much higher accuracy. Its only downside is that you can't rocket jump like you can with the rocket launcher (alt-fire function). And by the way, you might find rocket jump useful in tackling Phobos Anomaly in higher difficulties. When you approach the center of the second room the walls fall apart and monsters come bursting out right? You can use the rocket jump to quickly launch yourself back into the first room so you don't get surrounded. This is almost vital for builds that don't use shotguns or melee. Obviously, rocket jumping does self damage but it's a tiny fraction of the damage you'd normally receive with an ordinary rocket blast to the face.

Hell Arena should be easy and it only gets remotely difficult in HMP since that's when the hell knights show up. DoomRL's combat is hugely different from other roguelikes so here are some basic tips:

    1. Sound
    Turn your speakers up and listen for the breathing of the monsters as they move around. When you suspect a monster is in one place you can't see, don't be afraid to shoot blindly provided you have plenty of ammo. The monsters make noise when they get hit. You will be doing this a lot if you want to survive. Or you can just waste trait points with the level 2 Intuition trait which marks enemies on the map a couple spaces before they come into view.

    2. Corners
    You can shoot around corners, monsters cannot. If the monster is moving perpendicular to the side of the wall you're hugging, you're safe so just keep blasting them. Preferably with a shotgun so you push them back and prevent them from coming close. When they're moving towards you at about 60 degrees and less, they have a clear shot at you so you better get out of there and find the next corner and lure them into a preferable angle.

    3. Switching tactics
    If you ever get stuck in a shitty situation, like being out in the open and in the middle of two cacodemons, press tab to switch tactics to "running" and get out of there. You move a lot faster when you're running and you can dodge projectiles more easily. The downside is that your shooting accuracy is reduced. The more important thing is that the running tactic only lasts a few turns and you'll get "tired" once you've used up those turns (or once you've pressed tab again). Tired is basically just the "cautious" tactic, so don't worry about penalties, the only difference is that you can't run again until you either get to the next floor or you pickup/use a recovery item.

    4. "Serpentine, Shel! Serpentine!"
    When a monster is firing at you or about to fire at you, move diagonally from side to side as you run away from him (or as you run up to him if you're a melee guy). This greatly increases the chance (not guarantees) that you'll dodge the projectiles that they are firing. You will need to master this when you face the Cyberdemon in level 16. Or you can just use a BFG on his ass if you find it (easiest place to get it is at Halls of Carnage).