I see it all the time, the whole team ready to attack the castle and then one player who doesn't know how it goes spawns 1-3 slayers. I've noticed too if you can get on the guns in the enemies castle and shoot the boss it's a good way to distract him to take the tower. This challenge is a shame tho how it's basically forcing you to get MVP just to get the good weapons because all I've ever gotten was 1,500 happy stars. If the thing was really random I would get something different. What's worse is the special item is right after the 1,500 stars so it's like the middle finger to you each time.
^Sig made by Rajeanero