Zombie mode - bloodied Legionnaires try to storm a fortress and take their flag, then carry it back to base. Basically a one-way CTF. Everyone on one team attacks, everyone on the other team defends. The offensive team can only use Raiders whose movement capabilities are halfway between Raiders and Sentinels. This effect is dispelled upon taking the flag, in which the offensive team glows red and enters a "frenzy", giving all of them the movement speed of a normal Raider. Not sure what should happen if the flag is dropped, as instantly returning it to base is too OP and leaving it where it was dropped doesn't sound right either.
Or maybe Capture the Node, based (yet again) on Metroid Prime Hunters. Quote from a wiki: "The Nodes mode, scatters rings throughout the arena. The number of node rings depends upon how many hunters are in participation. Once you've occupied a ring for 10 seconds, it is yours. You do not have to stay within the confines of the node ring, to score points, you are free to roam around and capture other nodes. You get credit for your nodes as long as they stay in your possession and no one is attempting to steal them." Basically you capture locations that give you points periodically. You have to fend off the other team's players who will try to capture your nodes. It's like TDM with a different objective than just killing.