An evil idea when the PCs go a-pirating

[pennywit]

Once the PCs have completely overwhelmed the opposing ship, and it looks like all is lost for the opposing ship ... a mage there sends a fireball high into the air, where it explodes without hurting anyone.

(Two round interval)

A fireball explodes in the air, from a few miles away ....

[Inspectre]

It would need to be a significantly difficult enough fight the first time around so that the players don't go "oh boy! TWO ships to loot!" But I like the general idea. Always need to have something to keep the players on their toes, even if it's actually just smoke and mirrors to scare them.

[pennywit]

Some players will realize it's a signal immediately. And some players will go, "Why did they explode a fireball in the air and not hurt anyone?"

[*Khan*]

My players plundered a low in the water merchant vessel lately.
full of oozes (Sewer ooze) and captained by a oozemorph shifter and some Old sailors who has lost their sense of smell.
After the PC stinking victory they plundered the cargo… 2 plunder of “The best organisation fertilizer” for truffles (boar s~~%). The greedy players carried it down in their own hold as the merchant vessel was in to poor shape to keep.
The also found 5 barrels with a “private label” on them.
2 of them contains Roiling oil oozes - a nasty fight.
The players later sold the fertilizer on Bag Island, but the mood of the crew was low.

Stats on the ship:
Merchant Ship - - Kelpie's Crossing - - (Andoran merchant caravel)
DEFENSE: Init +4, AC 16, touch 2; Hardness 5, hp 810 (sails 480), Save +9
OFFENSE: Maximum Speed 120 ft. Ranged; crew 20 light crossbows +3 (1d8/19–20), 1 standard
catapult +7 (6d6), CMB +10; CMD 20, Ramming Damage 5d8
CREW: Captain Polly Threeteeth (CN female human oozemorph shifter 5) Profession [sailor] +10;
First Mate Ketra Semoo (CN female human rogue 4), 20 Sailors , 10 Sewer Oozes , usually below
decks in the bilge), 9 hp 17 hp
EQUIPMENT: 20 light crossbows with 200 bolts (mobile), 25 boarding axes (weapons locker), standard rudder, standard keel, ram, standard sails; heavily patched, sturdy hull, 60 squares of sails (two masts), Cargo 2 points of “The best organic fertilizer” for Truffles (Wildboar s&*#) Hidden under the Waste are 5 barrels labeled "Private".
Polly Threeteeth: AC: 18 To Hit: 5+3= 8 2x Slam dm: 1d6+3 Fort: 5 Refl: 6 Will: 5
Hit points: 40

Poorly maintained and lacking obvious defenses, the Kelpie's Crossing looks as though it tries to avoid pirates by being too poor to attack. That's true only up to a point; those who board the vessel can find themselves stepping in a slick of oil which then tries to eat them. Polly can get the cooperation of oozes and keeps a number on the ship.
The reputation and the appearance of the ship is such that few will buy passage or transport for their goods on it. Polly can be a willing accomplice in underhanded or illegal schemes for the coin to keep it sailing.

If chased Kelpie's Crossing sail sharp against the wind hoping the stench will scare off potential pirates. If they are still chased, they dump barrels/loot over the sides.
The 5 barrels under the fertilizer are kept on board. They are 3 barrels of Rum and 2 barrels of Roiling Oil Ooze, which attacks if opened.