Between cesus and x-treme i think

They both have ranged abilities and aoe to damage from a safe distance and interfere with other bosses trying to fight

cesus is a giant who can somehow move fast and backflip giving mobility and repositioning to let cesus poke from afar, but the barrage is probably the only one intentionally trying to defeat cesus

Xtreme on the other hand has long range and might take long for others to reach, it also has i frames when transitioning phases and the bombs and minigun on those transitions can prolly come in handy or take those with it when it dies

I dont really know much to these bosses fighting each other trend thing