You could do both. Describe the character's abillities and such then describe(in a fan battle if you wish) how that person would use those abillities for victory.

Example:

Auron:
He has high strenth but low speed. His abillity Power Break could lower "whoever's" strength.


Battle
Auron stared at his foe. The "other guy" began to run at him. His power was so huge, he would bash Auron's head in. Auron used Power Break and with it the "other guy's" strength was lowered helping Auron throw off his attack.

Got it?