We know what the Mask of the Shapeshifter is supposed to do, but does anyone have any information on the other items in the pack: The Cape, Lute, Needle, and Bicorne?

I am thinking they should have some functionality but I don't have a good idea of what they might offer the character who uses them...

Good question. I'm also curious.

These are the items in the Treasures of Rivellon Pack.

Mask of the Shapeshifter

Cape of the Red Prince

Lute of the Merryweather Bard

Needle of the Outlaw Rogue

Bicorne of the Sea Beast

I recall that at one point I read that the mask of the Shapeshifter was a usable item in that it could cast Disguise Self or something. No word on the other items, but obviously it would be fine if the Lute was just a Lute, and the Needle was just a regular dagger and the rest is just clothes.

I honestly hope that the mask doesn't do anything and they are all just cosmetic items.

I wonder if the mask of the shapeshifter completely replaces the disguise self. Obviously the mask will take the head gear slot while the spell would use a spell slot but are there any other differences between the mask and the disguise self spell?

If it is like the other similar items, and I suspect it will be, it would be a once per long rest disguise self spell that you can use.

My own thought is that I'm less concerned about whether they provide abilities rather than being simply cosmetic, but more that I don't want one to be strictly better than all the others. I'm fine with them all being cosmetic, and I'm fine with them all being useful. I'm not as happy with one being useful and the rest cosmetic.

It would be nice if they just gave little bonuses that didn't make any more of an impact that items you'd find in the first act.

I'd imagine the Cape would add a bonus to intimidation or other Cha checks.
We haven't seen any bonuses on musical instruments, but maybe the Lute will give you the musical instrument proficiency, and/or add a song.
I'd imagine the needle is just a dagger with a poison effect.
The hat could have a simple bonus to a proficiency, maybe perception?