Leveraging Lethality
Bateman's excellent Facilitating Fiendish Fights should be considered a sister piece to this article. It is filled chock-a-block with good advice for running combat. It's geared towards fights in D&D and expects an attrition based approach to combat. This is fine when dealing with AC and the increasing stack of hit dice. More Lethal Games like Classic Traveller, Mythras, Delta Green, Violence, et al require some changes to approach so that not every battle ends in the PCs being a pulped mess on the floor.
Lethal Games
But D&D is a lethal game, you scream! Yes it is! Or at least it starts out that way. But as levels grow and grow D&D embraces an attrition based model of crawling where ever-decreasing AC and ever-increasing HP let heroes risk larger and larger crowds of monsters. 10 bandits against a party of 3 is an oh shit moment at level 1-2 in D&D, but by the time you hit level 4 that same group of bandits is a joke. 10 vs 3 is always going to be a hairy situation in a Lethal Game.
Player Considerations
Keep Your Head on a Swivel
Be doing what you can to keep awareness of a situation. Gather intel before you go into a location, question NPCs for information to get an upper hand, take notes, do research: anything you can do to understand the terrain and enemy better is an advantage.
Get your Ass Behind Something
You probably don't have AC knucklehead so don't go charging into the melee unless you've got a plan. In games with firearms get into cover! Throw tables, shoot through walls, demolish the environment to protect yourself.
Little Advantages Mean More
A +1 sword is a great find in early level D&D but drops off which is why the +2, +3, +4 and so on all exist. In these games the shallow health pools mean any advantage you can squeeze is gonna pay off. A +1 or +2 to damage can be the difference between a wound or a kill.
Sometimes You Just Gotta Shoot
In D&D due to the nature of how AC works you get moments during the melee to grab a potion or do something besides fight. In a Lethal game you should get all that shit done before combat starts because there is no AC/HP buffer to let you tank a round to cast or take a swig. Enemies are just as frail as you are so focus on taking them down! Or if you absolutely need a break find a way to disrupt or disorient them. Flashbangs, cloud wall, loud noises, throw a bunch of fucking paper in the air, do something to give yourself a moment.
Tempo, Tempo, Tempo
If you aren't setting the temp of the fight the enemy is. Do not let that slip from your hands or you risk a doom spiral. Ambush the enemy, overwhelm, confuse them. Don't let them figure you out or wrest away your pace.
Don't Retreat from a Black Eye
Lethal Games will make you wanna be a gun shy. An important distinction to learn is when you're beaten and when you're bloodied. A PC death or two in a large party might be expected in a potentially large combat or deadly combat, but retreating too early will mean that you have to recoup those losses when you were close to winning.
Combat is Just One Means to an End
Before committing to a fight consider what you have to offer or threaten the other side with. Perhaps they could be a powerful ally to a third party or their morale breaks when you show them the head of their commander.
Lockdown the Area
Area denial weapons are a boon in games like this. Shut down parts of the map with fire, bring the ceiling down to make a new wall: identify the good terrain and either claim it or deny it.
Establish Plans
Be on the same page as the rest of your team. Set up Standard Operating Procedures for how you enter a room, set up an ambush, etc. These save time and get people to act together which helps keep the force cohesive!
Violence Perceived is Violence Achieved
If you can convince the enemy that you shouldn't be fucked with all the better. Have them run away, part ranks, give tribute. Just make sure you can back up what you're saying at some point...
20 Paces
Learn what is honorable for your enemy, figure out if you can use that against them. Duels are very common and if you are confident you can win them then try to goad honorable factions into them.
Enemy Considerations
Gear Up
Enemies will always roughly be in the same ballpark of HP as players, so their abilities are what will drive their differences. Choose faction arsenals, spells, and abilities to make enemies easier or harder.
Responses
Don't just have the factions get meat grindered endlessly. Fall back, make a plan, bring in reserves. Desperate foes might collapse a tunnel if the PCs are tearing through.
Encounter Size Matters
Big groups of foes will make PCs run or think of ways to circumvent them outside combat. Roughly a 2:1 ratio of foes to players is what they can stomach before they start to feel overwhelmed. Consider this when keying rooms and encounter tables. If you have lots of entries that are horde sized that will make PCs engage in stealth, hit and run, and flee quickly to avoid getting overwhelmed.
Armor Problems
Increasing armor might feel like a good choice in games that use AP or other more concrete armor values, I would advise against giving enemies too much armor though as then every fight feels like a slog.
Objective Oriented Gaming
Not everyone has a background in tactics and that's fine! A good way to go about thinking tactically is to think "what is the goal of my group of monsters?" and pursue actions that help with that. If their goal is to push the players back, inflict damage and seize ground, burn the ground from under them to drive them back, bar doors, put down mines. Use your gear and troops to their fullest extent. Forgive sloppy choices! Non perfect tactics present a more believable foe.
Duel Them
Players yearn for the 1v1. It's a sick thing to do. Fight them and kick their ass!
Reputations Precede
As the players fight and win, their tactics will begin to circulate. Have smarter enemies anticipate these plans. Ex. Players love to bait combatants into hallways to use Chain Lightning, factions in the dungeons might start placing land mine traps at door ways or making fire bombs to chuck overhead to block off their retreat. Keep responses in line with the intelligence, tactics, and resources available to the faction.
Location Considerations
Put Some Junk Down
Empty rooms are never empty right? Fill those spaces with junk! An office has chairs, dividers, potted plants, vending machines... Put shit in your rooms so it can be used and broken!
Factional Map Knowledge
For each monster/group you have active try to think where they would want to fight. If a random encounter puts them in a room that would be a serious disadvantage they might run away. If morale breaks maybe there is an agreed upon fall back point.
Healers
Exploration spaces in Lethal Games are going to be limited by how much healing the party has available. Factions in the dungeon usually have some ways to mitigate harm and should be considered.