How should I set up and execute air battles in my session to avoid easy encounters?

Question

I'm running the Storm King's Thunder campaign, and we are at the portion where the PCs get an airship to travel around in, the airship is about 1000ft in the air. There are approximately 5-6 lvl 7 PCs, and they have 3 or 4 hard encounters a day. There are two wizards, a warlock, ranger, paladin, blood hunter, sorcerer, and fighter.

For the most part, they have had fun with the different weapons and enemies they have faced; however, I find that one or two spellcasting PCs have been using spells such as mind sliver, polymorph, and hypnotic pattern to defeat more challenging encounters, such as one with a roc and wyvern. They make the creature make saving throws with hypnotic pattern and cause the enemy to fall to its death, and using mind sliver makes it even harder, especially on low wisdom creatures like rocs. Or with the polymorph spell, they cause the enemy to become a fish or chicken and throw it off the edge, and since the damage carries over, it kills the monster. I realize it was legal and made fights funnier, but it does get annoying when it's happening in almost every fight. Are there any suggestions on how to keep them on track without them making every encounter easy?

I thought of giving the monsters immunity to these effects, but it just sounds like a bad excuse for me not being prepared.

Answer 1

Combat balance is always tricky, and airship-related elements can make it harder. I'll try to focus on the novel environment of the airship, since that's the meat of the question. But for completeness, a few issues about combat balance generally:

• Combat difficulty estimates (like a hard encounter, deadly encounter, etc.) are just that-- estimates. And not very precise ones. Further, the difficulty of an encounter is mostly defined around the likelihood of PC KOs. Even a deadly encounter is one that PC party is expected to win
• Powerful parties are powerful. They have lots of options to deal with a variety of situations, and one manifestation of that is that they can approach a given encounter in many ways. Some of those ways will make certain combats pretty easy for them, such as gaining access to Polymorph. With options like that available, an encounter may need to be much harder to suit those powerful options
• You are running a game for a pretty large party. 5 to 6 party members (and even up to 8!) gives a big edge in terms of action economy, and allows for lots of synergies between PCs (which tends to make combats easier). If you have that many PCs, you likely need to include more enemies per combat in order to keep things challenging
• 3 to 5 hard combats per day is below the number assumed in a typical adventuring day, and consequently it's not surprising if the party overperforms

Tweaks to ordinary combat-balance issues are covered pretty well in answers to other questions, and are not quite in scope here.

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Airship combat between individual characters and enemies can be tricky to balance

As you've discovered! If you can get enemies onto the deck of the ship you can have a pretty typical combat encounter, plus an obvious terrain feature that allows shoving enemies over the side to plummet to the ground.

But if you have flying enemies that menace the ship by flying around it you can start to lose terrain features and tactics that add variety and challenge to combats. For an easy example, consider cover: outside of using the body of the ship, cover is probably going to be hard to come by. This favors spellcasters and ranged fighters, who get to act like fixed turrets.

My preferred approach to combat between PCs on or in a vehicle and enemies that move around that vehicle (this includes airships, regular ships, wagons, mine carts, and so on) tend to focus on treating the vehicle as a unique environment which is a part of the fight(s):

• A rollable table of ship-related effects is a great tool to have, and can really alter player tactics. For example, if the airship suddenly rolls to the side PCs may need DEX saves to keep their footing or risk falling prone/taking damage/pitching over the side. Rolling a d6 every round or two to impose environmental effects like that can make a combat harder without fiddling with enemy composition, as well as adding variety to combats generally
• Flying hundreds of feet in the air offers unique opportunities and dangers. Does the airship have to fly through a thunderstorm, possibly creating a risk of lightning damage or driving winds? Can the PCs defeat the enemies and survive the harsh environment? Does the environment make certain strategies more or less attractive, by adjusting the potential risks and rewards? Can enemies weave in and out of clouds, breaking line-of-sight and attacking from unexpected angles?
• What are the enemies' goals? If they want to kill or otherwise impede the PCs, they might as well focus on damaging the airship itself. This can change combat from an HP-reduction grind into a race against time, and can also keep enemies out of easy reach of spells and ranged attacks. If the enemies want something other than slaughter, the fight being relatively easy for the PCs may not be enough to truly "win" the combat encounter
• Some condition exists that means things get worse until that condition is fixed. In one combat I ran, my players were in a small ship trying to escape from a massive Orcish warship, which had shot a large hauser-connected harpoon into their deck. As long as the ships stayed attached, orcs kept climbing across the rope to board the ship. The PCs had to fight the boarders and cut through the hauser or rip out the harpoon, or else the fight would (effectively) never end and they would eventually be overwhelmed

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Adventure-day design is a different beast than single-encounter design

Encounter design is always an art, and designing a challenging combat is different from designing a difficult adventuring day. A combat might be tough, but with lots of resources a party might be able to prevail. An adventuring day being tough, in contrast, means more questions about whether or not it's worth spending resources right now (for an easier current combat) versus keeping something in reserve for potential future combats, and surviving those later combats when the resources are gone.

And however easily your players dispatch threats in a given fight, if they have more fights they will eventually run low on resources and face much greater danger. More combat encounters per day, with fewer opportunities for rest, lead to much greater challenges for the party.

Answer 2

Admittedly, Hypnotic Pattern is an unusually powerful spell and one that can tip a combat, especially if the PC's outnumber the monsters. Before you resort to changing the fundamentals of that spell, though, or "giving immunity" to monsters, make sure you are running the PC's spells RAW. If you are not paying attention to things like range and timing, but just allowing the players to use spells because they have them, spells like Hypnotic Pattern are going to come off as even more powerful than they already are.

The sky is big - have you checked RAW range?

Unlike a "dungeon" or indoor setting, where most of the participants remain in spell range for the entire combat, the sky is a big, open space.

Mind Sliver has a range of 60 feet. Polymorph has a range of 60 feet. Hypnotic Pattern, for some reason, has a range of 120 feet.

But the roc has a flying movement of 120 feet! This means that it has a reasonable chance of remaining out of spell range until its turn, and then moving into range and making its attack, so long as its target is not immediately adjacent to the caster. For example, consider a Hypnotic Pattern caster and an allied PC standing on deck 20 feet away. If the roc approaches from the direction of the ally, it can start its turn at 140 feet from the caster (out of range of the Pattern) and still reach the ally to attack by the end of its turn. If it is a big ship and the PC's aren't clustered together, that may even give the roc the opportunity to both attack a PC and get back over the rail before the caster can respond. With a +13 to hit and an automatic grapple, the roc should be taking a PC with it. That should give the players pause - once their companion is over the rail in the roc's talons, hypnotizing or polymorphing it may mean that a PC will be joining the roc in plummeting a thousand feet.

Casters can, of course, ready actions to cast spells when the roc comes within range. But remember that readying a spell requires casting the spell and then holding the energy, which dissipates at the end of the round. You can have the roc circle the ship a few times before it moves in. Once the casters have burned through a few third and fourth level slots readying spells that are never cast, they may reconsider.

Also, is the ship moving? If it is not hovering in place, but moving at a certain speed and direction, the roc may be able to use that. By grappling the aftmost PC, for example, the ship might move 'out from under' the PC on its turn.

Flying combat takes place in three dimensions

Currently 5e movement rules largely indicate two dimensional thinking. But the roc is a creature of the air. What is to prevent it from approaching the ship from underneath, so that the casters cannot see it until right before it bursts on deck and grabs someone? What is to prevent it (besides masts - I'm not familiar with the design of the airship) from approaching the ship from above, and dropping from outside of spell range to the deck, taking some fall damage itself but possibly doing considerable damage to everyone it lands on?

Finally, not RAW but pretty reasonable and supported in earlier editions - the roc could start its turn at a higher elevation than the ship and gain speed by dropping in elevation as it traveled toward the deck, allowing it to move from outside of spell range into its attack range and back off the ship in one turn.

The GM describes the environment

In general, you should avoid changing the details of player's spells when you find them challenging to deal with. Players often feel a GM is being antagonistic rather than fair if they 'nerf' the player abilities - the one thing the players have going for them and can count on. However, it should be expected that the GM describes both the environment and its effects on the combat. Is the airship noisy and the roc a silent glider? Then it can likely sneak up on the ship at night, in a storm, or in a cloud - getting within striking range perhaps in a surprise round. When a roc falls, is it being buffeted by winds or just the air resistance of its massive wings? That could reasonably be considered something that would "shake the creature out of its [hypnotic] stupor" before it hit the ground. Have the players polymorphed an enemy flier into a chicken and thrown it off the ship? Chickens can fly - perhaps not well enough to glide a thousand feet to the ground - but certainly well enough to have a chance of unintentionally colliding with the hull, taking enough damage to kill the chicken, and resuming their original form long before they hit the ground.

Rather than trying to change rules to limit the characters' spells, try to rigorously enforce pre-existing RAW limits, expand the strategic options of the monsters, and describe the consequences of the environment in ways that don't favor the players.

Answer 3

You raised several questions, but some relevant information that was not covered elsewhere:

• RAW: Max falling damage is 20d6 (70)
  • A Roc has nearly 250 HP on average, so it eats a disintegrate of damage but it is still going to fly back up and toss that wizard off the edge in a minute.

If someone wants to edit this into one of their expansive answers, go for it, and I am happy to delete. Didn't want to leave the same comment / edit in multiple places