I think Possession game mode was also on Skulltag. It was a green rock which if you picked up, you had to hold as long as possible without being killed however the price was you could not use any weapons. It's a bit similar to Catch the Chicken mod but yeah, good times playing this mod! Shame it wasn't fully finished, last version is 1.4 but I think there should have been more things like fixing railgun beam (it was always forced white even if was changed to other colors) and possibly new game modes like CTC Tournament and probably Capture The Chicken!
CTC Tournament would be like normal Tourney but with chicken added in and Capture the chicken would be red & blue chicken instead of flags, much like CTC Team Deathmatch but without scoring points.