I think an option to change the difficulty in dungeons would be awesome, the difficulties could be

First mate- slightly weaker enemies

Captain- normal enemies

Pirate lord- Stronger enemies

Pirate king- Extremely stronger enemies

it would make dungeons like the labyrinth easier for the younger players while adding a challenge for the older and more farmed players, the weaker difficulty first mate could have a drop rate decrease while the harder ones would have a higher drop rate for no auction/no trade gear