What if we were able to trade monsters with friends? How well maybe something like this.
(1.) First you need to be friends for at least a week before you can trade.
(2.) Once it was a week and you have been friends you can then start to trade.
(3.) When you trade you have to make sure that it's the same type of rarity, like epic and epic. And so on.
(4.) This could have a cost in gold to trade this type of Monster like 100k gold depending on it's rarity.
(5.) Then you can have a limit on how many monsters you can trade a day. Depending on it's rarity.
I think this would be a cool way to make friends and for those who have a lot of monsters to spare they could share with their friends.