If you look at the little banner for the event it is a warthog but if you leave the menu and then open it again, it changes to some halo 3 concept art. It’s a red holding a shotgun and being lunged at by a blue with a sword and a fight is going on in the background. This is the image http://www.isaachannaford.com/2011/01/cover-of-art-of-halo-3-was-game.html and a link to a reddit post with a video of what I’m talking about https://www.reddit.com/r/halo/comments/rm4a6p/easter_egg_or_bug/