Ok let see if i get this right.
The 20, 40 and 80 stamina cost missions spawn bosses. All the bosses are Gyrappys (red caterpillar things).
Everyone that participate in killing the boss get the same amount of Corals depending of the boss lv (?).

Someone know how much coral you get for each boss?

By the way, I'm currently "farming" the 40 stamina mission (the 80 is to much for my teams), so if someone whant to add me as ally my ID is 900895765