This achievement is best unlocked on a later bonus wave, as they will have every unit available at your disposal. I recommend doing this during a bonus wave as you don't have to rely on unlocking a unit by luckily getting a present for one during a regular wave. In one of the later bonus waves, just go in order and make sure you summon one of each ally, and the achievement will pop. Here is the full list of allies just incase you want to keep track, in order of appearance on the ally bar; farmer, sword warrior, spear warrior, bowman, panzer samurai, priest, nobunaga, frostie the bowman, spear horseman, assassin, & takeda shingen.