Death wall lasers that one shot you, changing map hazards, Enemies no longer aimbot hit scan or target lead you, so their hit rate isn't guaranteed if you are moving, powerups that grant triple damage, round modifiers like primaries do quadruple damage but our heavy weapons get taken and locked. Team finishers to kill certain enemies, a boss that charges at you super fking fast and you have to make them crash into a trap and then you can finish them, a currency to spend during these matches on permanent power ups like cracked out intellect or recovery stats, jolt rounds for primary or special weapons, weakening and suppress rounds on machine guns etc. It would be a highly replayable, high adrenaline, activity that let's you skillfully take on hordes of enemies through carefully choosing the right buffs and pick ups between rounds, creating a synergy that will have god mode power levels when played right but debilitating debuffs on certain aspects that could cost you the match depending on whatever enemies or modifiers happen next wave. As for purchasable abilities, imagine getting a legendary tier buff that grants you two permanent Nova Warp dashes (for any class) and then later, you might find a buff that says something like "Whenever you perform any kind of Evasion ability, you emit a Shockwave that weakens nearby enemies within 15 meters." It would be a roguelike activity and I think it could breathe new life into the game because not only will players create builds for this activity but there is now an element of uncertainty and they have to adapt to whatever buffs and debuffs they get.