The Agile is a title quest given by the Councilor of any race's capital city. This quest is the second of the three title quests available to increase your dexterity. It consists of killing 10 Lizardmen and 100 Centaurs. These monsters can be found all over Agon and even on the 4 smaller continents. You may only get it/turn in the quest at your race's capital city (ou must have done the first part before you can do this one).
The reward is a permanent +4 bonus to dexterity. If you do all the 3 quests, you can gain a total bonus of +12 to your dexterity.