if you unlocked all monsters, recycle your monster locker and rebuild it but don't upgrade it.
if you don't rebuild it, then you can't upgrade/build housing/monster academy/ monster lab
i made that mistake
@carlosalopez people can only attack him if their on his map, for example do you think im on your map, and they also can attack him if they both have a lv2 map room, they just need to find him, and if they are friends (when i added hihihi03, he kept attacking me, but i upgraded my map room)
 "Backyard Monsters (removed)"){kind=icon}