- Gotten the scroll from the Evil Cleric in the forest ruins
- Talked to Tulik in Zachul
- Beat the Vampire in Myron to save it from invasion
- Got the talisman from the Dragon in the Talisman Dungeon
- Talked to the Great Sage in the mountain ruins
If one of these conditions isn't satisfied then Marsus will say:
I would only take the hardiest of all adventurers to face the danger ahead. You are still too weak.
Note that Marsus only checks for whether you've satisfied the conditions for beating a mission, not whether you've received your reward from King (although, this is a fairly moot point considering Myron is invaded only after you've notified the King of talking to Tulik).