how do you get 3 or more of a monster?
for 2 you can use the the village building with the egg and then you got a chance to get two of the same at the start just reload until you get them, for more than 2 you keep them as eggs in your inventory and then hatch them all at once
it is a bit of a handicap as you have to survive with weaker and less monsters the more you want to stack them and you have to pool aura to pay for the egg sense to gurantee you get the same