Egg MacGuffin with Cheese

A plot hook device to explain anything in your world ...

The Horn of Legends
The Horn is an ancient device , although it may be older (horn of the cosmic bull of norse myth maybe) it appears to be a ram's horn trumpet with a mouthpiece of gold.

When blown at a sight , which is the origin point of a legendary thing with a hint of truth to it (which certainly includes belief or tradition), the Horn will produce the physical living embodiment of that legend. 

Could be used to create Godzilla, the Slasher, Dracula, Superman, or any number of others .  If the Horn is sounded again with the Legend within 12 feet the legend returns to nothingness - but now has the ability to re-emerge on certain times of the year...