In last two quest, we have the story of captain flameheart. Good. Excellent (your game is excellent too i love this game so much i spend hours and hours) So in some next quest we could have captain flameheart who unleash a new world boss (like kraken or megalodon) a big bird like you could see in zelda the wind waker (SoT remind me this game) A giant flying bird who could throw flame and wind waves with his wing. To kill him you should harpoon him then shoot with cannon. Of course when he's dead he drops good loot also drops a mask to unlock another quest to kill flameheart for exemple.
After that and after somes update we could have another quest focusing on voodoo. With a main villain character inspire by calypso in pirates of carabean who's awake a big giant serpent who spawns on fortress island or another island you could create for. It's a ground boss which throws poison, bite you and attack with his long tail. You must be at feet to attack him (no ship for this boss) So using sword, pistols or cannon on the island. His poison is everlast. Be we could loot an antipoison on a hard previous quest for example or just eat everytime during the boss fight. That's would be epic.
(your next update for PVP and faction will be great !)
Thanks to develop this game so much ! Good Work !
