In contradiction to the Devil's Roar, you could add a region with a frozen landscape.
Digging treasure in frozen ground requires special equipment, eg.: gunpowder, special shovel or hamer to pound the ice before digging.
Pirates should slide over icy land, so it would be difficult to run.
Pirates could freeze if they don't warm by a fire or wear warm clothes or drink some Rum, you could carry a Grog chest with you?
Islands could be hard to reach by boat unless you use an icebreaker (figurehead?), gunpowder a way trough the ice or slide over it.
A sleigh could be used for transportation, just like the rowboat is used in the devil's roar.
Blizzards could pop up, creating zero vissibility.
A small story could be created about pirates who got lost and are stuck in the ice forever!
It should have ice caves with stalactites!
Skeletons should freeze a few seconds when you trow a bucket of water on them, so should players!
Some regions could be reachable by crossing breakable ice, if it breaks, the player drops to death or in the water, freezing.
The region should have a hammerhead shark!
Maybe new animals to capture like Seals, pinguins...
Frozen players should end up in an ice cube that could be broken by teammates to release the player from the icecube.
All of this is very simular to last added region so it would fit perfectly into the game.
