How to optimize a lot of network traffic

To put it simple, I worked on a MOBA(multiplayer online battle arena) game back in college and I had no time and skills to improve this part while making the rest of the game.

The thing is, besides having up to four players, split in two teams, the game creates about 20 small enemies per team that will fight the other teams on sight.

The last version couldn't even have these enemies sync'd(they were only local) and the players were barely working properly. The game was made using the Master Server and NetworkView for most objects.

I'd say I need some directions to greatly optimize this network part, so anything will help. Thanks in advance.