Just like those men in black reinforcement missions is it possible to have multiple waves (as in, lets say 3 reinforcements , 1 spawning every 5 turns or something) either for zombies which would make sense but I'm not sure how balanced you could make it (Id still have fun) OR like that one protect the VIP mission (which is honestly one of most fun missions to do for me when properly equipped) but the enemies come in waves rather than spawn all at once, you'd eventually either win by defeating a stupidly large amount of enemies OR you pull out if you can't handle it, I'm not entirely sure what the point of an endless defense mission would be, it's more of a what if scenario.