I've run up to 12th/13th level in 5e. In my experience, there are 3 sorts of interventions I use for making fights more challenging, mapping to:
1. Interventions based on specifics of the Encounter
2. Interventions based on builds/tactics of the Party
3. Interventions based on general concerns with the Rules/System
I'll hit quickly on each of these, how often I think they should be used, how you can learn to use them, and an example.
Encounter specific interventions
These are tricks, complications, goals, or anything else that is bespoke to that encounter. It emerges by thinking through the scene.
• How often? I use these as often as possible, keeping an eye on pacing and on my own effort/burnout level.
• How to learn? Best way I've seen is talking about your encounter with other skillful GMs, either forensically dissecting one that didn't go well, or helping you think through an upcoming encounter.
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Example from my games: A collapsing river cliff is unleashing waves of skeletons (monsters) that were trapped/fossilized inside, threatening to push PCs into the river.
Party adapted interventions
These are strategies to thwart specific powerful or problematic PC capabilities, and encourage players breaking out of habitual solutions.
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How often? I use these intermittently, sometimes more often, sometimes sparingly to not at all, sort of like salt.
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How to learn? Really combing over the character sheets, making mental notes of the PCs' capabilities during play, and then trial-and-error.
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Example from my games: Sharpshooter ranger dominating encounters being faced with a court audience where they're thrust suddenly into close quarters fighting.
General interventions based on rules concerns
These are things like "my combats are taking too long, so I halve all monster hit points" or "my sorcerer twinning this particular spell is wrecking my fights so I'm nerfing the spell."
• How often? Personally, I use these as little as possible and only when it's strictly necessary or clearly the best way to achieve a goal.
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How to learn? These require more of a game designer hat – good rules knowledge and thinking through potential domino effects.
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Example from my games: For a
certain style of play, this was effective: Increased dragon HP, but allocating hp by body part, with consequences for reducing a limb to 0 allowing for called shots and more creative flow.
- PC1 - Paladin 6, Sorcerer 4
- PC2 - Rogue 2, Wizard 8
- PC3 - Ranger 10
- PC4 - Sorcerer 2, Fighter 8
Looking over your party (alpha striker, mage, ranged, melee), I have some hunches...
- First glaring weakness is very little healing. Do damage fast and hard to them, and force paladin to spend action using Lay Hands or ranger using Cure Wounds.
- Second weakness (I think) is not a ton of high-mobility. Include greater distances (with verticality) that require PCs to close the gap, and force squishy wizard to consider Cunning Action: Dash to get there or sorc/fighter to consider Action Surge to bridge distance.
- Alpha striking specifically has a big weakness – imperfect information (unclear targets, wrong targets, decoy targets, inability to perceive clearly). Mirror image is a rules-as-written example of this strategy.
- PCs often tend to turtle around a paladin for save bonus, so strategies to break that up are great – 2-3 goals that require different PCs engaging with stuff on different areas of map, ongoing damage zones, mages with fireballs, weaponizing one PC, etc.
- Ranged monsters – either along with terrain hazards, distance, or even better other monster roles – will help to keep the threat on.
- Party is balanced, but anything that separates them or removes one of them from the combat – even for a round or two – will have an unbalancing impact that requires players to adapt.
