Example Beat the final Boss of a game Do Insane things In scores(Earn much points),times(complete fast The missionor something),Complete All Hard Achievemets Etc...
I don't think it really matters too much since completing an Easy quest has exactly the same result as completing a Medium quest -- namely, you completed it.
However, it might be nice to have one more designation at least for a warning for some of those really hard quests, like the infamous Sushi Cat quest or some of the Epic Boss Fighter quests.
