Black Futures was the secret act for Radar Fest.
Vennart is playing with The Beft, maybe a Biffy show or an Oceasize reunion? The bassist from Dillinger Escape Plan is playing with his new band Azusa, although now Greg's new project has pulled out, a Dillinger show seems unlikely.
My money is on Mastodon (if the band is headline size). Troy is in Europe playing with Thin Lizzy and Brent saw him play the other night. Half of the band in the continent, maybe the others are too. They have also just finished a Co headline show with Coheed. I've read a few rumours saying it could be Animals As Leaders - although they headlined Radar.
Quite excited for this, it's my first festival camping but I'm going alone and have never put up a tent before. Wish me luck (that's if I get over this cold in time).