City defence game mode. Reasonably hard, almost like the opposite of the vault of glass. The 'cabal' or 'insert species' have decided to move to the offence and a team of 6 guardians is left to defend the different levels of the city right up to the tower if needs be. Have multiple levels of defence which the enemies will attempt to break through and if they do then you must retreat back to the next line of defence and continue on there. You get rewarded more if you defeat them earlier. So the less defence lines the enemy breaks the higher the players chance of a reward. Of course if the enemy makes it all the way to the tower, the darkness consumes you and the game ends. Defence tactics rather than offence tactics would be interesting I think.