you must summon each different ally type at least once. the ones you get to use during the bonus waves (after every 5th wave) count as well. the needed units are:
farmer, sword warrior, spear warrior, bowman, panzer samurai, priest, nobunaga, frostie the bowman, spear horseman, assassin, and takeda shingen.
to earn this achievement faster, try to summon one of each ally during the bonus waves, that way you won't have to rely on finding each of the locked ones in presents during regular battles.