RPG Insanity

I cannot get the achievement. I have completed happy ending,  sub quests on top of goddess tower and heroes grave. I have all achievement except 100 missions complete. What am I missing?

In the menu's "Help" section, there's a useful entry about "Battle Missions", which is probably what you're looking for. Sometimes, you receive "missions" during battles (most likely some tiny white text somewhere below the action bar), which prompt you, for example, to defeat enemies in a specific way or using specific skills. I'm pretty sure you'll earn the achievement after completing 100 of these "missions".

That's what I was missing. For some reason I could not figure that one out, appreciate the help