Where do I find Beautiful Diamond?

[DepthWave]

I have been collecting all those "trade for money" items and have always thought:"But what, if I'll need them one day".
After the first DLC, I decided to sell them, and now I need BD for upgrading accessories' properties. I want to increase EXP gaining.

But I seem to have only one of this kind. Which monsters drop it?
I do not think wasting so much time for getting to fight Game Master and Last Judgement is worth it, because you have to complete a lot of other events to be able to participate in the needed fight. And I have already completed all those events for twenty times or more.

[SUN]

dlc 1 bosses

[DepthWave]

Thank you.
Today I have been though a lot of bosses - it is fun for me just to travel through the maps to fight bosses only. But I haven't visited all of them, so decided to ask, which one drops the material.

[𝔜𝔲𝔢]

DLC 1 endboss (Elemental Wizard & Grimodoom) and the normal games' endboss (both The GM and Last Judgement) :)

[AtoliTadaka]

Kill the DLC2 bosses that are the alternate versions that have the room with 10 chests in it after you kill them and you get one or two of them each time along with emeralds, sapphires and I think rubies but it's a pretty easy way to get mats you need as well plus a ton of other gems for selling at the same time.