/u/Koraine explained the situation pretty well in the SRD thread. The top active moderator, /u/Ranguesy, had his account hacked, and the subreddit went to chaos for about 20 minutes until he got things under control.

Here's a video of what happened and an image.

And from Koraine's comment, here are the mods that were added. One of them being /u/xdjkeemstar, who is the real Keemstar of Drama Alert. He made a thread and a few comments admitting to being a cuck. Here's an archive of the thread after it was deleted but still showing his comments. I saw the thread before it was deleted, and it just had the same message that pretty much all of his comments had, which can be seen on his profile still. Anyways, this is what he has said.

I'm going to be straight here. I am a cuckold, but I am also a white nationalist. I believe that whites have contributed more to humanity than any other race, space travel, anti—biotics the list goes on. But when it comes down to it, blacks are just better at fucking. Theres no shame in admitting this. There is no shame in admitting that despite the infinite intellectual and moral superiority of the white race, black cock is just better at pleasing women. The reason white women are turning from the cause and running to niggers is simply because they are not being sexually satisfied. Can you blame them? If you dont get enough to eat at home youre going to go out to eat. The only way to save the white race from miscegenation is cuckolding. My pure white wife is my angel, the apple of my eye. And I want nothing but the best for her. So every friday she gets to have her fill of big black cock. And our relationship goes on like normal. We love each other, and plan on having a child soon. She also shares my red pilled beliefs. Monogamy is a tool of the jew. Just give it a chance once. Its exhilarating. Theres something deeply majestic about watching a toned muscular black stud going in and out of a beautiful white woman. Try it once.

This is what the sidebar of the subreddit said during the hacking.

Another post was made calling anime fans pedophiles, with some users blaming GamerGate in the comments.

It all came to a happy ending when a mod post was made by Ranguesy clarifying that his account has been hacked, and he was in the process of undoing the damage.

EDIT: Another mod has stickied his own summary of the situation. https://www.reddit.com/r/osugame/comments/43hw8p/what_just_happened_a_summary/

EDIT2: Just noticed I forgot to add the thread where the hacked mod called the game a ripoff. I haven't bother to look for an archive of what it said. It's possible it didn't say anything. https://www.reddit.com/r/osugame/comments/43hp48/osu_is_a_ripoff/