there is no answer. it all depends on where it is, who it is, what it is... this is going to either a. be a never ending argument b. die quickly now or c. die slowly.
Mancer He uses energy from his foes, he absorbs the Pyromancer's fire for energy, and eats the undead for energy, truly the Mancer is the most revolting -mancer there is!
solarmancer, they gain constant energy from the sun, and they can absorb the sun's energy through the ground, and at night, there's always the sun near earth somewhere