I wish that someone would post how to get the star requirements for each of the missions. I only found out now that if you play the game a certain way, you can change the outcome of the story! I didn't even know that you could check these out when you select the stage in Story Mode.
Nintendo 3DS Friend Code: [odin] - [1521 2560 5828]
I imagine somebody will do it before long. Until that day, you can at least check out those objectives once you clear a kingdom's story mode. Heck, if you complete your objectives quickly, you'll probably get a few on the way.
You can see what the conditions are after you finish Story Mode when you go back to earlier stages. I've made a couple of videos on the more annoying ones, I might make more but I don't know how wanted it is unless someone asks.