I thought it might be a nice idea to have a single bunny or zombie per 24 hours to have a name that shows if you hover the mouse over it. This bunny or zombie would be clickable and finding him grants a reward- or maybe finding 10 generates the reward. Nothing huge, but something worthwhile- maybe a buff or flowerbed in a new colour. (Purple would be my choice)
It's prob too late for it to be implemented for Halloween, but it might be doable for the next Easter event.
The advantages to the players would be-
spending more time looking at their islands and so may find that elusive last collectable
gaining a new or extra reward
something new to do whilst waiting for builds, troops returning, etc
The advantages to BB-
players spend longer on their islands or in game
a new thing that shouldn't cost much in time or effort to implement
Also, it might be fun if BB were to allow players to name the Bunnies for each 24 hours- no reward but just for the giggle. My suggestion for the first bunny name is "BB_Ravel"!