Grief by Icedcave and more is a remake of the 2015 Geometry Dash extreme demon Slaughterhouse. In specific, it focuses on the 2015 version of the once top 1 hardest level on the Demon List. It is set to be verified by Doggie.
At one point, Slaughterhouse reigned as the top 1 hardest level in Geometry Dash for over a year. While we now know this was largely due to SpaceUK lying and hacking to keep the level on the top, this is still an incredible feat.
The expected placement of Grief on the Pointercrate Demon List is not yet known, but many speculate that it will be top 1 in its current state. We will have to see where it places after Doggie verifies it.
This is Icedcave's next big project, so there will certainly be a lot of hype around this level.