Playable classes are a feature in Sherwood Dungeon which alters the player's look. They can be changed at any time, have some customization options and have no impact on gameplay, as they are purely for looks.
The Warrior is a playable class and was from the earlier version of Sherwood Dungeon. There was only one option of changing team colors, but as the game update more options of hairstyles, hair colors, skin tones, armors and team colors were added.
The Valkyrie is basically the female version of the warrior. It is the playable counterpart of the Darkblood Valkyries.
The Dark Knight is the oldest class in the game. Sherwood Classic had this race as the only playable class and only the team colors could be changed on the character. Now the dark knight has many options of helmets, armor, skin tones and team colors.
The Skeleton is from the earlier version of sherwood dungeon. It is the class with the least customization options, only allowing players to change its color and armor (the latter actually refers to its bones).
The Viking is similar to the Warrior and has three customization options.
The Ranger is one of the two female classes in the game. It has all the customization options like the other classes, excluding Skeleton and Viking.