1. do a skull of destiny voyage
2. wear the soulflame mask - everyone got 1 when they log in
3. start the fotd
4. whenever u hear the ancient skelly sound effect, look around for a skellie with a lantern head. kill it. they spawn 1 every wave. And the next one spawns as soon as 1 is killed. - Or at least that's how it was in my own experience - when everyone was wearing the soulflame mask.

Do this until u kill 20 soulflame skellies. After fulfilling the requirements, the lantern received banner will automatically pop up. Go to ur equipment chest to use it.

If on a galleon crew, I think 1 fotd will spawn enough soulflame skeletons. If on a smaller ship crew, u might need to do 2+ fotd, especially if some crewmates refuse to wear the soulflame mask because it doesn't fit their look.