The setup for this Encounter is pretty straight forward as this can be used in many different ways. It doesn't need to be used as intended from the original adventure. This is basically just a pit of alligators. How the PCs end up here is up to you!
They can fall into it as part of a trap.
They might be tossed into it by another group or some bad guys.
Perhaps they are just moving through the sewer and run into a large open area full of alligators!
However they get here is up to the GM. The important thing is to use the scary part of this encounter, the water. Alligators in the water have a distinct advantage. They can move around almost undetected. They can splash out torches. They may even pull PCs into deeper parts of the water so they have to swim. This is a great opportunity to use a little different tactics to make a fun and interesting battle.
In game terms the alligators can move around the battlefield with Superior Cover (10x Character Tier) while underwater. This allows them to move around easily and be very difficult to hit if they are not actively fighting someone. If they are actively fighting someone, attacked them during the round, then they do not receive this bonus.
If they use the Combat Maneuver Knock Around they can pull PCs under water or into deeper water. If they move into water that is deeper then 1 Square then they have to swim. This means they can only move 1 Space for each 5 points on an Athletic or Nature Check. This means a roll of 15 can only move 3 spaces. A roll of 14 can only move 2 spaces.
You can read this to them as a bit of flavor to color the Encounter.
You find yourselves in a large open room. Moss and filth cling to the walls. A foul stench of fetid water emanates from the large stagnant pool of water in the center of the room. As you peer at the filth floating in the water it moves and shifts ever so slightly. Was there something moving in the water?
