Concept for my setting: Statues of Nuadens

I need a deity for my upcoming campaign that is a bit gamified. Something that is explicitly transactional and a bit malevolent. I came up with statues of Nuadens to do that:

Every city that reaches a certain size has one: a wooden sculpture of a satyr several times the size of the average citizen. Their sinister face is covered in leaves. All is foliage except their left hand reaching out. A hand made of silver clockwork. A hand that will animate if any sacrifice is placed in their outstretched hand, dropping the propitiation into the waist deep, rough hewn, ancient fountain these statues are always set in. A single word is etched into the fountain: Nuadens. Once the sacrifice is swallowed up by the earth beneath the fountain the clockwork hand rotates to its original starting point with a suitable exchange appearing in return. This offered exchange seems to always be related to the original offering in some way. Any person will only receive something in return from the statue once each day, with a new day occurring at sunrise. However these statues are willing to accept as many offerings as one wishes to give. 

No one knows where these statues have come from or what their true purpose is. Some people, usually religious zealots and city magistrates, try to destroy them wherever they are found but they have a supernatural ability to sprout back up unobserved, overnight in the same city in different locations. Most citizens tolerate them for their utility: the traffic they bring to the square they are on, the fresh water that seems to seep up from the earth wherever they are located at, and of course, the usefulness of the worship performed at the statue.

The worship occurring at these statues is seen as forbidden and deeply shameful by the majority of people. Even discussion of them can be seen as taboo. Supplicants furtively visit them hooded, disguised, or else by cover of night, but they must wade out through the water to the middle of the fountain in order to place their offering. Many mystery cults have sprung up around them offering secret knowledge of useful combinations of sacrifices to make to the statue to get certain results. Or, in more clandestine circles, these cultists provide the numbers and anonymity required to offer darker and more evil sacrifices. Some are even said to have processes for the resurrection of the dead by the statues... with the right sacrifices.

The oldest of these statues and fountains are said to have grown slowly with time and use. Rumors abound of secret grottos beneath the most ancient fountains where the faithful can hear Nuadens whisper their will to them.