Recently I Was In Onigashima And I Checked My map While Questing Then Saw A Dungeon That I've Never Seen Before. It Looks Like They're Still Building That Dungeon, As It Had No Final Name To It. Im Very curious And If Anyone Knows Anything I'd Like To Know Whats Up With This New Mysterious Dungeon.

I saw this a little while ago too. In JP that location is "針ノ山" which is harinoyama. If it were a の instead of ノ, it would translate to mountain of needles. Anyways, my chars on JP are only lv 20s, so there is nothing there for me either, but according on the JP website, it says inside there is a dungeon called "闇火の森" or forest of dark fire. There is no information on either in the JP wiki so I presume that they're not accessible yet, and if that's the case, EN probably wont see anything of it for maybe another month lol.
That's all I know.

Edit: Wrong kanji, fixed to 闇火の森 instead of 闇日の森.