How can a...

How can a Lv. 14 Mesmer/Necromancer take on his Lv. 20 Dopplerganger?

I'm just looking to get Alsitha Freit ascended so I can take him and Neriandal Freit (Main) to Cantha and what not. But I dont know how I need to go about taking him down.

Bring enchantment sacrifice skills that dont return/increase health, sit there and let the dopple kill himself? Do that with backfire for an almost sure kill.

What skills would that be then Sentao?

Backfire
Order of Pain
and minion mastery skills, in that order

Cast Backfire first to plop on damage.

OR take Wastrel's Worry and Backfire and just evade the attacks until it Backfires itself to death casting WW and doing less damage than Backfire (thus it dies faster.)

Wastrel Worry + Backfire + ORder of the Vampire (Elite, capture in Thirsty I believe) worked out perfectly.

All I had todo was cast Wastrel Worry first, backfire next and repeat when needed because he spamed all three of them, and Order of Vampire takes 17% of your health so needless to say he went down fast.