Instructions:
1. Spec demo and make sure you have grimoire of supremacy selected as a a talent.
2. Go to any class trainer and enter the proving grounds.
3. Start a proving grounds trial by talking to the panda.
4. Summon elemental
5. Cast rain of fire (this step can be skipped when you have a stack of 20)
6. Stop the trial by talking to the panda.
7. Repeat from 3 until you have a long enough buff duration.
UNFAIR.