i farm d2s2 with just my 3 heroes..
a good one to start off on is d1s2, drop your heroes/troops to the right of where the archer is
Yeah lately I do dungeon 2 skull 2, usually lose troops and maybe 1 hero but with luck they all stay alive, isn't nearly as smooth as d2s1 tho. Reason I'm trying to advance was to clear 50 to get the free gems
I'm still trying to figure out how to consistently clear d2s2 without losing one of my heroes, but usually i start from the tower near the shaman and go from there