Fire Magic: 15 (12+3)
Death Magic: 10
Energy Storage: 10 (9+1)
Fire Magic: Mark of Rodgorot, Immolate, Meteor, Fireball, Fire Attunement
Death Magic: Virulence, Soul Feast
Other: Ressurection Signet
Weapon and Armor:
I always wonder what kind of armor should I take on Arenas. There is only small difference between them - bonus vs. elemental damage. It's hard to say what kind of Elementalist you will face with so take this one you like. ;)
For weapon use Staff with bonus to energy and HP. Staff should have "Improve skill cast/recharge using Fire Magic".
How to play:
Right before fight cast Fire Attunement to save some energy.
Find some target (Necromancers and W/Mo can be harder because they often uses some regeneration spells) and cast Mark of Rodgorot on it. Now use immolate and Virulence. Foe should have -10 degeneration for quite long time. All you have to do is constantly activate Mark of Rodgorot by dealing fire damage. You can do this by Meteor or Fireball but also by your staff - it deals fire damage as well.
To heal yourself use Soul Feast but remember that you first need to kill someone. ;)