I created a similar minigame where I have "heroes" based off Game of Thrones characters where each player when they fight for the first time are randomly given one of the heroes, each with special abilities, immunities, fatalities, etc. They receive XP for doing HP damage and receive a boost of XP if they get the final blow (multiple people can attack a single opponent until that person is killed). Stamina is consumed on each attack and players can purchase items to improve their armor, health, stamina, XP earn rate, etc. Health and stamina regen on a time interval basis. People can purchase new heroes with points and level them up.
However, I don't use the Fight command for this. I think you are better off programming your own game from scratch like I did.