The very first session of my pirate campaign had sort of a level 1 boss fight at the end. But I should provide some context. Half of the group of players was locked up in a Kturgian* prison tower, while the other half had to climb said tower from the outside, to attach a chain to the cell, and rip it apart with the aid of a large ship in the water down below. But climbing back down the way they came, turned out not to be an option, because the alarm was immediately sounded, and guards with muskets started opening fire. The prison tower had gun ports everywhere, so the players would be sitting ducks if they climbed down the rope. So there was only one option left: To escape through the inside of the tower. They had to first acquire some weapons, and decide what other prisoners they would set free (if any).
(* A ruthless Turkish-inspired faction)
Once they had found some weapons, and freed some prisoners (who would join their pirate crew later), they would have to fight their way down, floor by floor. The prison tower was located not far from a rocky shore, and always in the middle of a violent swirling sea. Inside the tower it was a maze of stone spiral staircases, and bridges with no railings. Any wrong step would result in a very long drop and a short stop. So they had to treat carefully, and keep an eye out for guards with muskets on lower levels.
The boss battle
Right before they reached the bottom floor, they encountered a guard with two pet crocodiles. They knew that the sadistic guards would often feed a prisoner to the crocodiles, whenever they were bored, or grew tired of the prisoner. But other than that, they rarely fed the crocs, so they were very hungry. Now even a single crocodile is quite a fierce opponent for a level 1 party. But since one of the players was a Druid, I threw in 2 crocodiles, so that the encounter wouldn't be entirely negated by a lucky handle animal check. And they did indeed manage to pacify one of the crocodiles, which then turned on its handlers.
So now they were only up against 1 crocodile and what was left of the guards. I first had the crocodile attack one of the npc prisoners, just to show the players what they were up against. Much to my own shock, I rolled maximum damage, and the crocodile instantly shredded the npc in one attack. This made it clear to the players that this was not an opponent that they wanted to get close to. So the players used the staircases and pillars to their advantage. The entire building was designed in such a way that it encouraged the use of cover (since enemy guards would be shooting from other floors with muskets), and the use of bridges to funnel enemies into areas where they would be easy pickings.
The players managed to beat this encounter with few injuries, thanks to clever team work and use of the terrain.
