You can challenge anyone that is not currently in a fight already.
When you do challenge someone, state all conditions of the match in the first post. This way they know what they are getting in to before they accept.
Conditions can be anything. There is honestly nothing that is illegal in a coliseum match. If you want to ride a dragon then go ahead and state that. However, the other gladiator must AGREE with those conditions. Please use PMs for communication between players.
Please make sure your character is at the correct level for the match before beginning the fight.
Magic Items are tricky. As a house rule you are allowed two magic items. The items cannot be more then five levels above your character. So a level 5 Fighter can use a level 10 sword. Additional magic items must be agreed upon before the match begins.
List ALL equipment on your character sheet.
Once you both agree on each others equipment then go ahead and fight!
I understand that this is a lot to go through for a fight that might not be very long. Feel free to do multiple fights with the same characters. Best two out of three would give you a little more for your money!