I don't know what to use....

... to clean this really important old family toy.
It's a wooden duck, and when I was younger I colored on it with marker, and when I showed my parents they were really upset. I tried to clean it, but it only came off a bit. I got upset and put it away a few months later I tried again and a bit lebih came off. However, there is still alot left on it, and now none of it will come off.

Does anyone know what I should use to clean it?