How to Rule a River Rapid Encounter?

[KOLE]

(ZAK W, DON'T READ IF YOU HAPPEN TO BE BROWSING)

Hi.

In a stunning example of layers finding the ONE THING you hadn't prepared for...

Players did some spelunking, going through a terrifying failed lab of alchemical/transmutation experiments that was hidden in a dark cave. Due to reasons, the Dragonborn Supremacist wizard running this cadre of horrors knew the party was coming, and had been preparing while they took a short rest and took another hour trekking through his horrible managerie of failed experiments. He took this time to collapse most of the cave (which lead to the hideout of his secret dragon cult hideout) and burning all his research notes, ensuring the party wouldn't discover his true intent. After doing all this, he drank a potion of water breathing, and threw his last yellow diamond to summon an earth elemental to open up a small river with the intent of flooding the entire cave.

Despite rolling repeatedly behind the scenes, the earth elemental did a surprisingly terrible job of opening up the damn, leaving the Wizard to make a final stand. But he's smart, and a powerful spellcaster. He had an escape plan, but had to know what force he was up against.

On the player side, the entire party is starting to realize the terrible, diseased ridden corpses they've discovered used to be people, and IC and OOC are massively bought in to take this bastard down. They engage him, and pull of some amazing tactics I didn't see coming.

I forgot the Bard had Faerie Fire... So there went the "drink potion of invisibility and cast fly to escape" plan. In desperation (IC) the Dragonborn plunges into the massive river, vanishing in it rapid wake.

I thought this would be the end of the encounter. Nope. The halfling rogue jumps in after him. We left the session there.

I did not intend for this session to happen. I figured the party would either catch him in the middle of preparations, causing him to bring the earth elemental in to bring the cave down mid combat, or he would succeed in flooding the cave and escaping. The party taking a short rest threw a monkey wrench in my plans, and the earth elemental rolling TERRIBLY didn't help. When I decided the wizard jumped, I figured I would roll after the session to see if he survived and figure it out from there. With a PC involved, however, I need some fair rules to figure out what happened.

They are level 3, so still pretty squishy. Player understands the move was risky, and is okay with it resulting in his death, but both him and his character REALLY wanted to finish the job.

So, TL;DR I have a seriously wounded evil wizard and a fresh low CON score Halfling Rogue being pushed by a raging rapid through a narrow, choked funnel of jagged rock. How do I determine what happens next?

[Blood of Gaea]

Off the cuff, I would have them contest an athletics check each round, if the Rogue wins three times, they catch up, if the Wizard wins three times, they get away.

Every other round, do a Con save to see if they can keep it up, go with 5, 10, and then 15. The first fail gives them disadvantage on their swimming check, the second fail halves their speed, and on the third fail they stop moving and go under.

Also, on the third round make them roll a Dexterity (Athletics) check to avoid hitting a large-sized rock, if they do, they take 2d6 damage and automatically fail their next Athletics check.

That should make it wrap up pretty quickly, but be pretty action-packed.

[Keravath]

One key difference is that the dragonborn has consumed a potion of waterbreathing while the halfling hasn't (based on the description). This makes a huge difference when trying to make it through a raging torrent of water in a cave. There might not even be any air for the halfling to breath and even if they catch the wizard the halfling will drown while the wizard will not.

I'm also a bit confused about the situation. If the raging river was being used to flood the cavern, how is it possible to jump into it to try and escape? It sounds like it would be almost impossible to swim upstream at all unless the character was exceptionally strong and had a swim speed.

Finally, does the wizard have any remaining spell options like teleport or a strategic use of misty step/gaseous form or something else that might allow them to manage an escape?

[Demonslayer666]

Just make it up.

I agree with the athletics check (or checks if you prefer) and taking some damage. That way the player has a chance to succeed but risks drowning.

The river could go outside and maybe the rapids ease up, and there is a horse, foliage, fog, or something, allowing the wizard to escape. Or maybe the wizard knows of a secret chamber and disappears into it.

You could also have them encounter something else that the wizard slipped by.

[Telok]

Wisdom - Survival or Wisdom - Vehicle (raft/kayak/canoe) to read the river for upcomming hazards. Strength - Athletics (swimming) to move yourself around.

Make a random hazard table and check for each round length stretch of the rapids. Rollers, holes, strainers, sharp rocks, drops, and no hazard will make for a decent 1d6 table. Look up the kinds of dangers on a white water canoeing site. Holes and strainers will be strength checks to escape and both stop movement while calling for a Dex save or start drowning. Rollers and drops probably have a Con save to avoid being stunned for a round, maybe a 1d6 of damage. The sharp rocks are the only one that's straight damage.

Movement will be either to go faster down stream to catch the guy, lateral moves to avoid dangers, or pull off into an eddy behind a big rock for a rest, better look down stream, or a stealth check. I'd do distance by section of rapids. Start the target off three sections ahead. Each swim check forward moves you into the next section (closing distance), avoids the current hazard, moves next to someone in the current section (when people are caught up), or pulls into an eddy for a rest stop (stop going down stream until you leave the eddy).

So you're looking at each round roll a hazard. Everyone checks to see the safe path through. Everyone chooses to swim somewhere and/or do something else. Apply the hazards based on success/fail of checks. Then do the attack/spell/grab actions. This sequence pushes that the river is more directly and constantly dangerous than just a standard fight, keeps everyone moving, and still allows the usual fight stuff if you need it.

[Man_Over_Game]

Stealing some aforementioned ideas, you could have both creatures make a Constitution (Athletics) check to see how tired they get from trying to swim at the start of each round, with the Mage having Advantage from the Potion of Water Breathing. The DC increases by 5 each round, and failure means that the creature suffers Exhaustion. The creatures act normally in turn as they try to gain distance against the other.

[CapnWildefyr]

Everyone has posted a lot of good ideas. Adding on, if the elemental is still around, have him reappear, roaring up out of the water. He slaps at the halfling but his huge ham fist misses... unfortunately the wave from the slap sends the halfling backwards out of the water. Dont let a roll kill your adventure, it sounds like a lot of fun. Roll anything and announce 'boy were you lucky he slapped you back onto the shore you only take 5hp". Your evil overload can now use fly to escape, or for that matter, you dont even have to explain anything that happens behind the scene here as long as its fun, escape is plausible, and the party does not feel swindled. A big elemental ought to help in that respect if they are only 3rd level.