At the tavern, you can hire yourself out as a mercenary to guilds.
You can sign up to be a mercenary at the Tavern. There, you can adjust the slider to the pay you would like to have per battle. The minimums and maximums of the slider increase as you go along. When deciding your pay, take into account that there are many other mercenaries out there as well as the fact that you may receive injuries in these battles.
Once you are hired, the mercenary page will change to a countdown timer to the battle. Guilds recruit mercenaries to fight other guilds. On this page, you can find out which guild you will be fighting for, which guild is the opposing side, whether you are attacking or defending, and when the battle will take place.
Guild Battle Edit
Once the countdown timer reaches zero, you will receive a battle report about the guild battle. You will also receive all the damage you took from the battle. The report will show which side won, the damage each side dealt, and how many knights participated in each side. This should not be too important to you. After the battle, you are re-registered as a mercenary automatically and you are allowed to change your pay or quit the service again as you wish. The battle takes 24 hours and on the menu you see which side you're on.
During a guild battle, your knight will be damaged, due to the fact he's battling, so be careful not to participate in quests or other duels so you don't run out of health.