Voilà j´ai trouvé ces astuces sur Gamespot mais je n´ai pas essayé (dite moi si ils marchent):
-Pac-Man ghost in mission 16A:
In mission 16A "Desert Arrow", the ground is mostly desert with lots of circular patches of green (farmland, I suppose). One patch is in the shape of a Pac-Man ghost. To find it, go to grid section 5D (upper left grid is 1A, with numbers going across and letters going down). It´s in the northern middle section of the grid.
-Special Commemorative Message:
Upon completing every mission on the Ace Difficulty while obtaining an "S" Rank, you´ll recieve a special message from the developers during your final debriefing.
