The Mob Battle Mod is a fun addition to the game which lets you arrange mob battles. It’s really easy to use. Just select the mobs you want to fight and they will soon get started. Now you and your friends can host your own gladiator battles and make bets which mobs will win. Pretty fun, right?
Then long-tap each mob using the Battle Mob Selector item to select the battle champions. The item can be found in your creative inventory.
You will hear a short pling sound when selecting each and when both are selected a long pling sound will be heard. As soon two mobs are selected they will start fighting each other.
In this case the iron golem on the right appears to have been the strongest and most skilled fighter.