What can I do with pearls?

If you have a blacksmith, you can forge your troops.

Also you can forge your towers, obstacles and spells.

pearls were useless for the first 2 years, now they are the point of the game.

Pearls are very useful especially to forge troops and spells. Troops or spells which have been forged many tiimes can become much more powerful than they are without forging. 

And also to forge your hero items 

Buy items in Granny Shop but its not recommended,forge your items like Legendary items to transform them in Uber items at +3,forge your troops stats like : damage,HP,speed,etc… forge the spells to up stats like damage or range or reduce cooldown or add like in Toxic Cloud Slowdown effect,etc… Forge your defense towers stats

Before you ask how forge work or others stuffs I prefer to explain to you directly at the same time. When you build the blacksmith each level add a melting time more your blacksmith are high in level less its the time needed to melt items.

To obtain pearls there is many way : 1.The melthing slot are important more slot you have and more pearls you can obtain to melt a items. By example at 1 slot you have only 50% means a ring can give you 1 pearl with 2 slot I think its 100% that means the same ring give you 2 pearls. 3 slot at 150% the same ring give you maybe 3 or 4 pearls. 4 slot at 200% give you 6 or 7 pearls etc…More you have slot and more pearls you get to melt

  1. you can also obtain pearls in COF( Chamber of fortune) in a chest

3.Spending gems. I don’t know the ratio something like 100 gems = 20 pearls 500 gems = 100 pearls or something like that 

4.Participate in ninja Event. Whatever you finish Rank 1 or Rank 100 you obtain pearls

5.In every chest : Some chest can give you only 5 pearls and other can give like Legendary chest a Legendary Pearls like 45