how about a local coop mode (just within the same network the other person is connected) where the players raid maps 3-4 times the size of the regular ones (that way 2 players wont clear it in less than a min)
and somewhere around that map is an entrance to the boss fights (the old unused(what a waste i dont see them anymore since i started mapping, especially since these bosses have actual attack patterns), and new ones)
(no trade, will cause problems)
or make your friend a hireling, and that person gets rewarded with loot whenever you finish a map
- hireling “friend” scaled down to same lvl as main
- hireling “friend” can only be hired by one person (else everyone will be sharing the same most meta built hireling)