I think a vendor should be introduced that can sell specific outfits and boat customizations that are themed after the large monsters.
Killing the kraken could cause it to drop a kraken tentacle or some sort of body part. You would retrieve it like treasure from the water after the battle and turn it into this vendor. The vendor would exchange it for a form of currency that could then be used to buy clothes, weapons, and boat cosmetics that are themed after that specific monster.
Collecting and turning in fresh kraken tentacles could be traded for abundant kraken teeth, and then said teeth could be used as a form of currency to purchase kraken sails, hull, cutlass, etc.
The meg could provide an eye. Again you would have to kill it when it appears and collect the eye from the corpse like a skull and return it to the vendor in exchange for shark teeth or meg teeth. Those teeth being used for the set of cosmetics that are megalodon themed.
This would be a perfect opportunity to make the meg figurehead obtainable again for people that weren't part of the first event. Instead of fighting the meg once during the event, you would have to kill multiple ones to earn eyes and earn the currency needed to buy it.
We have gold and bilgerat doubloons and this would add two more forms of currency plus more for any new monsters introduced and integrated so an alternative is have factions or a faction.
A monster hunter faction that goes to 50 like the other three, increasing by turning in monster parts. Cosmetics not bought but earned either through leveling up or earning commendations like turning in 1/10/100 meg eyes, or kill a meg with a gunpowder barrel.
It's known that these monsters become no more than an inconvenience after seeing them enough times so this would definitely help create a reason to fight, kill, and even hunt these two and any additional monsters added later.
