Gems of War

this achievement seems daunting, but its actually not too bad since required XP doesn't ramp up to ridiculous levels until you pass lvl 1000. The pain in the butt part is getting the proper creatures traited up and hero weapons. Spending real money is not required.

the fastest way to gain XP is by farming trait stones which you get by playing explore. Every kingdom has an explore mode that can be accessed once the quest line is completed.

edit: the difficulty selection has changed. Difficulty doesn't effect xp gain, so you can select the easies (difficulty 1)

hero weapon:
Black Manacles (you will eventually wind up with this weapon through levelling)
-OR-
War and Peace (you will get this from the Khaziel quest line)

armor:
lion armor gives highest bonus at 75% bonus XP. This armor costs 250 gems
I would recommend using either Dragon or Celestial armors instead. Both of these give 50% to xp gain, but also give bonuses to gold and souls. these armors require 500 gems to buy. The 25% difference in XP is actually insignificant.

hero class:
the following classes give + 5 magic to brown magic when raised to lvl 20 and have traits that start a game at 50% mana.
Mechanist (Adana) (clockwork trait)
Thief (Zaejin) (fast trait)

banner:
slayer banner (Dhrak-Zum's) or any other with ++ to brown.

creatures:
you want creatures that have the trait stone link. this gives +1 mana for brown matches. the effect does stack and you can even use 3 of the same creature with it.
following creatures have stonelink:
Acolyte
Autumnal Imp
Blast Cannon
Dwarven Miner
Ghoul
Golem
Marid
Sand Cobra
Soothsayer (<- this guy is very useful for farming if you get all his traits)
Sunsail

spend gold to level following kingdoms to 10 (each gives +1 to magic):
Blighted Lands
Darkstone
Karakoth
Silverglade
Zul'Kari

basically make brown matches and fire off your hero weapon. You will rarely have to use your hero weapon more than twice. It is @5-7 wins to level until you reach 1000. These go by very quickly once you get the + magic kingdom bonuses and mana traits.

other ways to bump up XP gain:
blue guild statue (up to %50)
pet lucky (from 1% up to 5%)
guild war event: 100% xp bonus for 24 hours if your guild wins the previous day

good traitstone/XP farming teams:

(one I currently use)
Fire Bomb
Sunbird
Hero (any class) Imperial Jewel
Forest Guardian

clockwork sphinx
sentry bot
tesla (<- 1 use of her skill usually wipes out all enemies)
mechanist hero w/war and peace

Tesla
Holy St. Astra
Hero (any class) w/black manacles or war and peace
any (Falconer would be good choice)