My players were in a boss fight, in the belly of a Greatship.
One of the players had shape-shifted into a winter wolf, and had a Frostwind Virago in a grapple. To make more things more interesting, I had her shift herself and the person touching her into the dark fairy realm. Only after defeating her, was he able to return to the normal world.
Meanwhile as the players killed off a couple of my Azarah cultists, I had one of them deliberately attempt to sink the ship with a water spell. The ship started tilting forward, water started rushing in, and one of the players ordered his crew to try and keep the ship from sinking. And they did so, by grounding the ship on purpose. But another cultist dove into the water and got away. The players guessed that the cultist simply dove into the water to flee the ship. But little did they know that the cultist was actually making a dash for the gunpowder room.
I counted down the rounds, with a general idea of how many rounds it would take the cultist to reach the gunpowder. After the time was up, I had a nearby npc inform the players that he just saw that a cultist run towards the back of the ship with a torch. The players instantly knew what was about to happen, and dove into the water, just as the entire ship was blown to pieces in a spectacular explosion.
What also made this situation interesting, was that not all of the enemy pirates knew of the plan to blow up the ship. In fact, they were deliberately not told what the mad cultist was planning to do.