Question

Is there a reward for the Mystery of the Valley Quest? If so, what is the reward?

Answer 1

The reward for the Mystery of the Valley quest is the Guardian Statue:

 

You see a guardian statue. It weighs 9.00 oz. Mending the fragments of the guardian statue's crystal, a potent energy emits from its core. Letting it shine in a bright and mystic light.

As of now, there is no use for the statue, it can be used as decoration on your house, but maybe it can be required for a future quest regarding the Monk vocation in the future.

Source: https://tibia.fandom.com/wiki/Guardian_Statue_(Quest)