Chests are the most popular methods to help unlocking characters.
There are 2 different types of chests, but each type has 2 different colors.
The Pirate Chests are the 1st type of chests. The #1 is brown with golden handles, with a logo of swords and a skull on the front. The #2 is also gold with golden handles, but with a logo of bones and skull on the front. However, the #2 also has golden coins next to it.
The Sea Chell Chests are the 2nd type of chests. The #1 is purple with a white stripe in the middle, along the logo of a purple sea shell on the front. The #2 is grey with a white stripe in the middle, along the logo of a brown sea shell on the front.