Each AI is piloting two races, vastly increasing the amount of units that will be fielded.
Mode select between a very normal experience or with my extra events, triggers, added unit spawns, and resource bounties. Events include a certain amount of dynamic difficulty control. If you play in single player with events on you are provided workers for all three races to enable you to ever produce enough units to live.
You can download the map here: https://www.dropbox.com/scl/fi/w5m29ha1r96p9mzvx9xuo/Impossible_Assault_II.scm?rlkey=1fy6r4kadooxj79v1uq79tkji&st=awpiudyw&dl=0
If you're curious about the first one, I posted about it a long time ago here: https://tl.net/forum/brood-war/591691-new-very-high-difficulty-co-op-ums
Hope ya'll enjoy it!