I have a Mage who wields more power than any other (think a hundred thousand normal Mages). He gathered an army of cat warriors from the Guderian forest to his banner and attacked the Kingdom. The cat warriors are bound to him via his powers (he has the power to control all living things except humans). His armies are besieging the last human-controlled city in the kingdom and it is on the verge of falling. My hero has set out on a quest to stop him by slaying him.
The Mage lives in a tower of vines and trees that he grew using magic to accelerate growth of his plant tower. He has no guards because he doesn't need them. The area has a similar flora density to the Amazon rain forest in Brazil. My hero has to somehow kill him, despite the fact that almost all the material around him is alive and is therefore can be placed under the direct control of the Mage.
Anyone can use magic, but very few have the strength of mind to use it. In my world there is an afterlife and the dead are constantly trying to return to the Earth. They try to get into people's bodies and hide from the Spirit Guards there but usually most people have strong enough minds to unknowingly kick them out (even children do).
However, when you use magic it takes away from your bodies natural defenses and you are left vulnerable, both physically and spiritually to attacks. This wizard has been using magic to extend his life for ten thousand years, making him the oldest and most mentally well-built of the Mages. My hero has the limited ability of a level 1 wizard (meaning that he only has the ability to use telekinesis and fly by casting vocal spells).
Spirits are almost totally no physical although they can control fog to make impressions, they can not speak or hear. There are numerous magical artifacts, one of which our hero uses called the Flaming Word of Türbrik that can start flames, shot said flames, and control existing flames with its own magic, although it cannot make large flames it can start them and control them once started.
The forest itself is magical naturally which allows the plants and natives to channel this energy for their own purposes. The Mage can control the plants which in turn control a virtually infinite amount of magic within a fifty foot radius.
How can my hero defeat this life-controlling Mage in his own environment? Also assume his maximum range is 100 feet and we are working with medieval tech levels. Take note that as long as conditions for plant life are good he can sped cell growth of the plant up to near infinite speeds.