I still need to figure out how to play BerserkRL properly myself. Hahahaha...
Hmm... well, I guess I can talk a bit about my own strategy...
I'm a huge fan of the running ability, but it only becomes really useful if you upgrade it, so the first thing I do is take two levels of Endurance and max out Running ASAP. A lot of my gameplay involves running ahead of the mobs so they don't surround and overwhelm me. It's impossible to avoid damage altogether, like in DRL, but I do what I can to mitigate it.
My strategies for individual enemies:
Imps: Kill them fast with the crossbow; run a step away from whatever I'm fighting to do it. (I don't like being hit from a distance while I'm trying to stay ahead of the mob of melee enemies)
Bulldemons: Watch out for their charging ability. I never stand exactly two squares from them in any direction, because I know they will charge and hit me for large damage. If I approach them, I always stand a knight's move away and let them come to me.
Mandagores: They hit hard; they hit very, very hard, but they're slow! I never take on more than one at a time if I can help it. Of course, in later levels, there get to be so many of them that I don't have a choice, but by then I tend to have more ability to keep ahead of them. They heal themselves by eating other enemies and it can be entertaining to get them to eat Bulldemons, but it's generally advisable to avoid going toe-to-toe with them if possible.
Scavengers: They heal themselves by eating corpses, so I try to lure them away from any corpses before fighting them. (Of course, as the battlefield gets littered with bodies, this gets harder and harder to do over time)
Phasehounds: I like to prioritize hitting them, not because they're more dangerous, but I only have to hit them once and they teleport away. They're the "I'll fight you later" enemy. :D
Ice Devils: Like imps, but more dangerous because of their freezing ability.
Yetis: Like Mandagores, but more dangerous because they only appear on ice levels where you move slower. (Side note: I hate ice levels) :P
Treespirits: Kill them fast. They have the ability to bring trees to life and turn them into Treants. The Treants themselves are very, very slow and easy to avoid, but they hit very hard and it's just generally better to have fewer enemies on the battlefield. (Treespirits can also teleport, which can be a bit annoying)
Wraiths: They like to raise their own personal army of Skeletons. The Skeletons themselves are slow and not too hard to fight, but it's easy to get mobbed by them, so it's generally good to take out Wraiths fast. Wraiths seem to be resistant to the Crossbow, so I often have to expend a bit of energy to run up to them to melee them to death, usually trying to do it in a position where there's a wall behind them so they don't get knocked back away from me and I can kill them quickly.
Defilers: The spores they launch aren't worth fighting, because they're immobile and explode on their own without any intervention from me. It's tempting to just leave the Defilers alive, since I can lure enemies over to the spores and let the spore explosions hurt them... but the other ability of Defilers is to infect enemies with a disease that makes them explode when they die, so that makes them potentially very dangerous, so I tend to prioritize killing them. (Though not quite as highly prioritized as Wraiths, for example)
Blizzards: I didn't even know they were a thing until very recently. I've only encountered them twice, so I haven't figured out how to deal with them consistently.
Demons: It took me a while to realize that their crazy names actually mean something! :) I've been trying to figure out what each of the prefixes/suffixes mean and here's what I've got so far... (I'll spoiler tag it in case anyone wants to figure it out) :)
Each part of their name refers to an ability that they have. Here's what I've got so far:
Ian - Imp projectile
Nar - Mandagore consuming enemies ability
Tur - Bulldemon charge
Hee - Fast (Like even if I'm running, it's hard to stay ahead of them)
Ab - Resistance to crossbow
Keh - Scavenger's ability to heal by eating corpses
Gon - Defiler spores
Da - I'm pretty sure this makes them more likely to evade melee attacks
Qua - Phasehound blink (teleports)
Nod - Wraith's raise skeleton ability
Also, all Demons (as far as I know) can heal themselves slowly. Once you start fighting them, you're going to want to prioritize taking them out.
Some general notes: Keep an eye on the "pain" display; if it gets too high, you won't be able to hit anything, so it's best to back away until the pain goes down; personally, I don't bother trying to fight if it goes above 3.
Also, periodically, you go berserk! :) You can tell when this is going to happen by looking at your hitpoint metre. When you start, it's all light red and it gradually changes to dark red over time. You go berserk when the dark red part reaches your current level of hitpoints. This makes it a bit of a catch 22 about when you go berserk; if your hitpoints are low at the time, it will last longer, but you will also be closer to death. There are a lot of benefits to being berserk, like you do more damage, you take less damage, and you're unaffected by pain and freezing, but you can't reload your weapons, so use them sparingly.
Well, I guess that's my strategy guide for BerserkRL. That's probably more than you were asking for, thelaptop, but hopefully, somebody will find it useful. :)
EDIT: (Sept 18, 2018) I don't know if anyone will read this, but I added on to the Demon name section. :)
EDIT2: (Jan 13, 2020) And one more for the Demon name section!