Collectable Mob Heads

Imagine having Collectable Mob Heads, this would prove as a valuable collectable all mobs would drop a unique to there type of mob head. I thought a cool way of this would to use the moon cycles you may not know this but Minecraft does have these, so why not Minecraft create there own Lunar Calendar for all the creatures of Minecraft! (Excluding boss's and mini boss's) So basically all mobs get a month each and during every Minecraft month, if a mob of that month is struck by lightning they have a chance of dropping a collectable head. This also means the damage of lighting is increased and players might have some sort of way to tell what mob month it is. (And might have some other game mechanic to get there head with) 

Side Note; I personally always thought every mob in Minecraft should drop a collectable head, because why do only the creeper, skeleton, wither skeleton, zombie, ender dragon and Steve have a collectable head?