This is a very simple, yet very effective stradegy, for elementalists. Its Easier if you are level 20, but any level will work, as long as you have enough attribute points to max out atleast 1 attribute. First, max out Air magic, get it to 12. Drop all you skills, and equip Blinding flash, and Glyph of lesser energy. Take only these 2 skills, and a weapon, preferably a wand with high +energy, and an item in your other hand with + energy. Ok, when you go to fight dopple ganger, immediatly hit the "c" button, and cast blinding flash. turn so you can seem him. start attacking him with you weapon. Cast glyph of lesser energy whenever possible, to conserve energy during the fight, for blinding flash. Everytime blinding flash wears off, cast it again, and keep attacking. it will take a while, but it will get the job done. with blinding flash, their is a very low chance that he will hit you. He doesn't use blinding flash on you either, so you have nothing to worry about, using this stradegy. I have personally tried this myself, and it is VERY easy to defeat doppleganger, using this stradegy, however, you will need alot of energy, so you dont run out while your fighting him.