Swimming Rules for 13th Age, Part One

Because tactical movement tends to be abstract, the 13th Age Roleplaying Game takes a light touch toward such fantasy staples as mounted combat, flying, and swimming. Perhaps not coincidentally, those are topics most game designers tackle under duress, because it’s easy to get them wrong—and almost as easy to get them right but make them unfun.

Even though we aren’t under duress, we find our 13th Age characters dumped in the drink often enough to offer these somewhat-sketchy, wholly unofficial swimming and underwater combat rules for 13th Age. Try them out yourselves, and let us know what you think in the comments.

Design Principles

Let’s talk scope. Do we want to cover the entire breadth of life under the sea? Should we model water pressure and ambient light as the PCs dive deeper? Do we want to treat everything from weapon velocity to bleeding wounds to vocalized speech realistically?

Um, no.

Let’s focus on basic rules for the key moments that tend to crop up in typical d20 fantasy gaming:

  1. Character suddenly dropped into the water and must get back out without drowning or being swept away.
  2. Characters forced to fight undersea enemies with no warning.
  3. Characters intentionally exploring an underwater environment on a longer-term basis (beyond just one encounter).

Let’s also also talk depth—rules depth, not water depth. It’s not a game about swimming; it’s a game where you occasionally have to swim your way to the good stuff. So let’s design just enough to make swimming and underwater combat feel different and dangerous, not necessarily realistic.


In the first case, we’ll lean on the skill system. We want our rules to model two things: swimming in hazardous waters (ocean swells, swift current, crashing surf, and so on) and holding one’s breath. Not every encounter will feature both. Sometimes you have to swim through the flooded hallway, but the water is still. Sometimes your longboat capsizes near shore, and you’re battered by waves but not drowning.

Swimming under ordinary circumstances is automatic. Yes, even if your character is from the desert or the Elemental Plane of Air or whatever. Forcing rolls for ordinary movement gets old at the table really quick. As for extraordinary circumstances…that’s where the environment DCs in Chapter 6 of the core rulebook come in.

Adventurer Tier Hazard
rolling ocean waves DC 20
Mountain stream current (swift but shallow) DC 20
Champion Tier Hazard
Shore breakers, deep ocean swells DC 25
Swift current, few chances to grasp edge DC 25
Epic tier hazard
Tsunami-level waves DC 30
Pressurized water (geysers, clockwork plumbing apparatus) DC 30

Note that the backgrounds in 13th Age are more specific than just a “swim” skill; as a GM, you’ll need to use your judgment on what does and doesn’t apply. In a pinch, let characters use their Strength modifier in place of a relevant background.

Let’s add one key wrinkle that makes the wizards and sorcerers (probably poor swimmers) happy: a –2 penalty on the check for PCs in light armor and a –4 penalty for PCs in heavy armor. If they don’t like it, let ‘em take a round to disrobe from light armor and two rounds to get out of heavy armor.

Holding Your Breath

Let’s charitably rule that all PCs can hold their breath for a minute, just because we want to enable fun things underwater—however briefly—and realistic breath limits shut off more interesting story moments than they enable.

Unlike many other fantasy d20 games, 13th Age doesn’t have a robust saving throw system where attributes (Constitution in this case) and level are meaningful inputs. But it does have PD, which rewards high Constitution, and we can let hit points stand in for level (mua ha ha ha). After the minute is up, drowning (and asphyxiation if you’re stealing these rules for a dust storm or outer space or whatever) begins to take its toll.

At the start of each round, make an attack against each drowning character’s PD, according to the following table. If the character is fighting or swimming, use the high exertion option:

Tier Attack Bonus Damage
Adventurer tier +5 3d6
Adventurer tier, high exertion +10 3d6
Champion tier (didn’t get a good breath beforehand) +10 4d8
Champion tier, high exertion +15 4d8
Epic tier (enemy is magically trying to force water into you) +15 3d20
Epic tier, high exertion +20 3d20

With these numbers, drowning is a serious risk for everyone, but tougher and higher-level characters can last longer underwater.

Once again, let’s add one wrinkle. In real life, near-fatal drowning has a host of long-term consequences. But in the fantasy fiction that underpins 13th Age, characters often spend a few minutes coughing and spluttering after nearly drowning, and then they’re right as rain. To model this, declare that using recoveries (including healing magic) to restore hit points lost from drowning is twice as efficient; spending one recovery heals twice as much.

If it’s an underwater combat situation where drowning people are also being stabbed/bitten/magicked, you can either track combat damage separately from drowning damage (not a big deal, because it doesn’t come up that often) or just say to heck with it and let all healing in the quick rest after the underwater fight count double (also not a big deal, because you’re a GM and have plenty of ways to take those hit points back later.

With swimming rules and drowning rules in hand, we have everything we need to cover the first use case we outlined above.

For the second use case (an underwater battle) and the third use case (a long-term underwater adventure) we’re going to lean on the damage types already defined in the rules and on some new magic items. Look for those in part two, coming soon!