The Princess

The princess is a NPC that you can find. She will give you a quest and reward you with coins. There are two different quests :

Find three roses
You just have to gather the three roses that are somewhere on the map. You don't have to look for them in any containers. Sometimes they can be destroyed by explosion, so be careful !

Find the Ring Diamond
You have to find her Ring Diamond. It will be in one of the treasure chests in the level.

Reward
Gold.