The data reaper is a series of Hearthstone reports put out by an organization called Vicious Syndicate, a group of elite Hearthstone players and personalities, all of whom are dedicated to accruing the most up-to-date data on the Hearthstone ranked ladder at all levels of play. This includes ranks Legend through 25, and it even includes both Wild and Standard formats, though the Wild data reapers usually take a bit longer to update considering the popularity of the format compared to Standard.
Above all, it’s nice to have a resource anyone can look at, that’s publicly available and for free, that you can use to look up the meta in Hearthstone. The game itself is such a meta-dependent game, in that you need to have an up-to-date understanding of each of the decks that might ravage the format in order to best understand what’s going to hose you down in a few minutes. If you’re not aware of the decks, you won’t know how to handle their aggressive or controlling strategies, and thus it will prove difficult for you to figure out how to beat them. It’s a simple sort of dynamic that Vicious Syndicate has created, and speaking as someone who’s never reached Legend rank but has gotten close a few times, I would be nowhere without those people and their resources. I regularly send my data over to them, though I don’t play enough for it to be that relevant, unfortunately. I hope, in the future, should I play more and eventually reach Legend, that the popularity of this website continues to grow and eventually lead to even more advanced strategies and builds for decks. Even now I’m pretty sure people are still optimizing the decklists that are put out by VS, and people will make them their own in their own different ways.