On the ship as megadungeon
Microwave guns: requires two emitters carried by different characters: where you cross the beams, the water gets locally boiled (leading to battlefield “smoke” of a cascade of bubbles). Range: up to 100 yards, damage: 1d8 per round, doubling every round you fail to move.
Bubble gun: blasts air bubbles at the target, but these ones are sticky: if they attach they lift you up. If you can form a big bubble around your enemy’s gills you can suffocate them. Anyway they totally destroy battlefield visibility and sonar.
Concussion Grenades: does what it says on the tin. 4d6 damage over a 10′ radius sphere, 2d6 for the next 10′
Depth charge: or shallow charge, for the benthically inclined
Phosphor flares: cause burns, blindness (or light up the depths, depending on your orientation)
naive map from a round the horn oceancrawl
Charlatan has of course been on this kick for a while. He got me to say this:
Encounters: what about the classic siren call and/or illusory voluptuous form concealing the dead thing below?
Or the illusory ship, that lures greedy characters into the deep (but maybe only after they take something off it, echoing those stories of mutineers who loaded their pockets so with stolen gold that when they made to swim away they sank instead)?
What about the ship that sails right up over land to exact its revenge, like in the legend of Cruel Copinger, carried off from his bedroom ashore by a revenant flying ship?
Fire ships that conceal their flames below decks or which burn down from the mast-tops in mockery of earthly gravity (and St. Elmo’s fire, either a ward against undead or in the hands of the damned as a weapon).
Or ships that constantly re-enact their wrecking – in which case the hazard is immediate if you’re on board, or may come from an unexpected angle if you’re still on your own vessel, and the ghost ship drives you onto the rocks.
Monsters: Davy Jones’ shellfish crew was one of the things I liked most about the PotC films. In a similar spirit, how about:
– multiple-amputee undead like the man-of-wounds but adapted to the perils of the sea – with hooks and peglegs and whales’ teeth and sharkbites?
– poltergeists armed with a chandlery of shipboard stuff – handspikes and blocks and strangling ropes and sail-darning needles and boathooks and flensing spades and, worst of all, anchors? The poltergeist could operate in creepy-everywhere mode or could cobble together a walking, wheezing form out of on-deck junk to wave the characters off.
And finally, I promised you a ship as megadungeon. Apart from the decidedly Miyazakiesque Grande Chasse Foudre (great lightning chaser, that is), what about:
The hollow iceberg: up top it’s just a hollow in the floating ice that keeps going down. Below it’s an ice-crab warren of passages, all transparent and refracting like a hall of mirrors, that keeps getting darker as you descend. Your torches, alas, will get extinguished by meltwater if you don’t keep moving them.
The Marie Celeste as dungeon – first there’s sheer scale: the giant deserted ship represents a massive treasure, but only if you can bring it to shore. But what about the wood-bound world of the ship that reveals a mythic underworld below decks? Mysteriously much larger than it should be, leading into a stinking orlop dungeon, with gardens of valuable plants and arks of animals and everything else you find in bottled worlds – including collectors.
Sometimes the cargo is not just the treasure, it’s also the monster – the most famous example I guess is Alien, but ships often carry dangerous goods that shore kingdoms won’t tolerate (plagues and vermin and other causes for quarantine, to say nothing of political prisoners, weapons or pharmaceuticals). So your adventurers break into a barrel and they see this strange hairy blue fruit inside, and they don’t realise until too late that it requires sunlight to activate it, and before you know it the deck’s awash with these:
You know how ripening bananas release a hormone that ripens all the other bananas (and everything else) nearby – an exothermic process that leads sometimes to ripening room fires? In 6 hours the smell and heat become overpowering – sweet, alcoholic, headachy. In 12 hours you have a temporary army – they run amok, then fall down after 2 days and seed themselves in the ground…
But it’s maybe best simply to multiply the number of decks below the waterline, for a slow-release cumulative horror realisation that the players are getting in too deep – every level is just as claustrophobic as the last (say, 150′ long by 36′ wide), but they get progressively stranger as you keep going down.
It could go all psychological like Bluebeard’s castle* (after all, if the house is a map of the mind, the ship is, as Foucault said, both a womb and a psychopomp for going beyond the horizon), with rooms of bizarre purpose. Bartok’s version starts simply with a torture room and armory, but goes on to reveal a “sea of tears” and chambers of mysteries too terrible to be sung about.
Or it could simply be unreliable – the bottom planks so rotten that when you step on them they break and let the sea in, the ladders twisted and rat gnawed, so you risk falling down them, the spars and rigging just waiting to fall on your head, every cask and box in the cargo hold a trapped chest containing god knows what.
* the Blackbeard/Bluebeard clash suggests a Battle of the Beards that I find irresistible: legendary devil pirate vs. psychological suppressed violence auto-horror – FIGHT!