From ROI Wiki

Proxies are any living creature or lifeform, including living machines, used by either Meshua or Negago as intermediaries or "proxies" in their war with each other for control of the universe. This is because, per their agreement from long ago, neither side may directly engage each other (this was requested by Negago himself, as he's not strong enough to directly take on Meshua and win), nor directly attack or harm anyone who is not their own personally chosen proxy, or they will, by default, be forced to forfeit the war and surrender themselves to the other party. Some well known proxies of Meshua are Psial, Yazik, and the Burgon Lions. Some of Negago's best known proxies are the Vandros, Ferrel Black, the Margog and the Horde, as well as the Midazin.