classic - no changes
rebalanced - autoheal, allied transports, rally point, easy multicast
double race - can train both peon AND peasant in th, so basically you can get ogres and paladins, blood AND heal both etc etc
(ironically its possibly the most balanced game mode of all, because everyplayer can get access to any unit, spell)
blizzard - unit stats from remastered, mostly archers and their upgrades was changed
triggers - if hosted map with triggers they are used, if map not have triggers then secret war2mod game mode enabled where basically all existing triggers work (mostly used for testing)
ogre mode - playes from same team can control one shared base and units
its separated because can be played together in other game modes
also not only 2 players, you can even play 7v1 where 7 players play as 1 base