Right now, the ritual skull is only used for activating Fotd. However, in this purpose it is superceded by the skull of fate, which makes doing Fotd much easier. Therefore, I propose more uses for ritual skull (and skull of fate, but why would you?). Perhaps pirates could use it to perform a ritual at islands with the greymarrow spawn table. A ritual skull combined with another trinket or item could produce some sort of effect.

Ideas:

Temporarily marking all ships on the server for you to see, like how reaper emissaries work but for all ships

Fully recharging a weapon loot item

Turning a collection of cannonballs into curse balls

Turning some standard loot into ashen loot

Or, it transmutes the skull into a different item, like a skull of fate, or

A one use item to summon a megalodon

An item that shrouds any tracking on your ship for 20 min or so

An item that stormproofs your ship for like 20 min or so.

Really, just any other use for it other than fotd. It is a cool item that I don't want to turn into trash loot.