Combat makes up a decent chunk of most campaigns and the setup can make it either a blip that no one will remember to one of the most memorable parts of the campaign. I've been looking for various ways to make combat more fun in my campaign and was eager to see if people here have any ideas they'd like to share. I'm looking for anything that gives alternate win conditions, gives the players new ways to interact with the environment, forces special behaviour or anything to make a combat encounter unique.
I'll start with some of my favourites.
Battle Complications
Anything that makes combat more complicated than "kill this list of people". Special conditions and anything in that direction.
-- Ritual in Progress Someone is casting a terrifyingly strong ritual and it must be stopped by either destroying conduits, removing sacrificial materials or killing the casters. Typically this is something that allows enemies that wouldn't be very dangerous otherwise to have a far greater effect simply because the party can't focus them down, needing to spend their time on the ritual being stopped. If they fail, the possible punishment should sound quite bad, so that they feel a strong urge to stop what is happening.
-- Ritual-borne Foe Similar to the last one, but this time it's not a time limit but rather something that requires a novel way to defeat. An enemy that is incredibly powerful and dangerous to the party being kept alive or present by as summoner or necromancer of some sort, or alternatively by a contraption. Players must destroy or deactivate the source to defeat the opponent before it defeats them. This may be through directed combat or through a puzzle of sorts in the middle of combat.
-- Constant Reinforcements The BBEG is constantly calling forth fiends from another realm or some device creates more and more small creatures swarming the players. These elements make sure that the players can't just clear out the room, leaving the big bad guy in the middle helplessly overwhelmed by sheer action-economy. Instead, they have to either win quickly or alternatively do their best to disable the sources of enemies.
Environmental Hazards
These are difficult to design but great when they work out. Hazards in this case is taken in a very general sense.
-- Unstable Ground The ground that both the players and enemies are standing on is unstable and may break away easily. May it be as the result of some level being pulled, an attack hitting the ground or maybe just random chance. As long as the players have some chance to react to what is happening, this can include anything that can make ground unsafe to simply stand on. This makes certain types of ground that are stable very favorable and possibly worth fighting over. Bonus if the enemies have ways to contest ground, just like the players can.
-- The Floor is Lava The ground erupts in Flame, flashes of radiant beams hit the combat arena or meteors strike the area. Very similar to unstable ground, but more temporary, are occasional AoEs hitting the ground. Once again, these are best when the players feel like they can really work around them sensibly.
-- Bottomless Pit (Maybe with a bottom) A pit that people can be thrown into. This urges people to finally realize that shove is a thing. Don't make it too easy to fall into though, falling to your death into such a pit with little chance to safe yourself won't feel great. Make sure that they get a chance to save themselves or be saved if they do fall!
These are what comes to mind immediately. What interesting mechanics have you used to change your combat into something the party ended up finding really thrilling or memorable? I myself play DnD 5e, but I would love to hear your stories from other systems that I may implement in my campaign too!
Alternate win conditions is my favourite way to spice up combat, although I think it's important to drop a healthy amount of normal fights to the death in, because many characters are only at their best when outputting damage.
On top of that, considering that if you make the goal to calm a rampaging giant, the bard with a suite of enchantment spells may find that trivial while the barbarian may have nothing on their sheet that can aid them. One solution is to introduce interactive objects such as a voice amplifing horn on a roof to speak to the giant, but that still favours mental and social skills, which will favour spellcasters in the end.
My piece of advice which I'll swear by is inelegant but has always worked for me; ensure there is something dynamic in the encounter that dealing damage to is good. Perhaps it's knocking down a monument to block a road and cause the giant to steer (in terms of telegraphing something like this, just tell your players it's an option, you don't need to be cryptic), but the monument is guarded, making an ettwmot to knock it over more dynamic. Better yet, make the giant unable to be calmed because a band of unselie pixies and quicklings are slashing at his back and legs, and those quicklings work for a fey antagonist to the game. Suddenly the characters who are built to be dynamic can stil ltry to charm, convince and steer the giant, but the PCs made to deal damage can simply battle these fey. Assume the party are reluctant to kill the giant because they need information from him, or he's a friend.
The distilled version of this idea is this: "the PCs have aim A, dealing damage will either not help them achieve it or make their lives more difficult once complete. An antagonist force is causing the stakes of aim A to rise, so aim B is to thwart them, and in this case, damaging them is fine. That's a format that is vogue enough that using it multiple times would often go unnoticed.
One other suggestion is a little more complex; have a series of dynamic encounters all related to the same goal. This goal can be lifted from a game such as capture the flag. Suddenly splitting the party is fine as your paladin may stay in one room to guard your flag (or totem or whatever) while your hasted monk dashes ahead to capture your opponents. Alternatively, it's a bomb planting goal. An arcane explosive must be planted in a room to disable to infernal portal, but each point is guarded by cultists. As your party arrive in room A to take control of it and plant the bomb, the cultists in room B rotate round behind you, and now you must defend room A. Perhaps you give the arcane bomb to your rogue and tell them to hide outside room A until the party attack B, and when the cultists rotate leaving A unguarded for the rogue to sneak in and plant the device.
This latter option is always fun to do but it's really important to consider that if your party don't typically have many encounters or don't often delve into dungeons they'll come up much less often, and that's fine.
My final piece of advice is simply to ensure that you have at least two kinds of enemy that function very differently, which could be as simple as archers and knights. You will always have dynamic encounters because no battle will ever play out the same.