https://kotaku.com/bloodborne-enemy-went-undiscovered-until-2017-1820656029

https://www.youtube.com/watch?v=PkMPCScnhpU

This find has quite a history, as is explained in the video. 

Miyazaki himself presented the first footage of the Chalice Dungeons at the first ever PlayStation Experience Convention in December 2014. Showcased in the footage was most prominently an Undead Giant with two blades for arms, one of which is on fire, enabling him to set the area around him as well as his victims aflame. 

Bloodborne then released in March 2015, but the Flaming Undead Giant was nowhere to be found in the dungeons. Along with other things such as Boss Rush and the Revered Great One's Coldblood, this version of the Undead Giant was generally declared as "Unused Content", that is, not having made the final cut of the game. 

Three years later, on 19th November 2017, a group of Tomb Prospectors, led by KolbrotKommander (the creator of the dungeon) made the impossible discovery by officially sighting the first ever Flaming Undead Giant in a Depth 4 Cursed and Defiled Root Chalice. And so it goes full circle. 

wow the chalice dungeons keeps giving extra content after all this years

I wish the Chalice Dungeons weren't so boring.

Technically it wasn't undiscovered. It's just the first time someone uploaded any footage. If you got the platinum trophy, you 100% ran into this enemy before.

I doubt it because it wasnt listed in any Bloodborne wiki i think

The thing about Dark Souls, Demon Souls, and BloodBorne is that every creature is weird looking and after a while it is whatever. Plus there is so much hidden areas to view and it is a very hardcore game. This is so obscure that 99% of the BloodBorne players will have no idea. Not to mention this enemy doesn't give you anything in particularly rare so it is hard to gauge.

Im pretty sure i fought that thing myself... wish i recorded all the chalice boss fights but i only bothered in doing so with the bosses on the main game.

Not necessarily. The chalice dungeons have almost limitless possibilities for how they’ll go, and you only have to do a select few for the platinum. I remember encountering several new enemies in the dungeons well after I achieved platinum. You might be getting confused with the enemy that basically looks the same, but it’s claws aren’t elemental

yeh no i saw this guy atleast twice already farming chalice dungeons. i saw a bunch of ppl on reddit say the same.

the only item noone has found yet is this one.

Still not found within the game in legitimate way. First mentioned in Collector's Edition Guide from Future Press. Only way so far to acquire this item is through "PS4 savefile editing".

Kotaku had an artcile about that: https://kotaku.com/bloodborne-players-are-still-looking-for-secrets-in-the-1790770464

absolutely right! i saw this guy on the way down to the queen when i was working on my plat and another time in a root chalice farming run.